I kinda figured you'd take it the wrong way.
So here's the long answer.
Again, your rough idle issue throughout the rpm range can fall into several categories.
The basic three are problems with:
b.) fuel delivery
c.) engine internals.
Spark plugs fall into the first category; I have tried the Bosch Platinum 'Plus' plugs and had disastrous results.
These engines only have 3 plugs, so even at $8 bucks a pop (ten years ago) I figured why not treat my engine to the best. That was before I knew about this forum. After lurking for years, I joined because they were pretty decent in their response to my question about cam shaft gear differences.
So after reading the general comments, I found I wasn't alone in my experiences with that particular Bosch plug.
Certainly, no one is bashing Bosch products; the fellows more experienced (not me) are trying to steer us on to what works, and what works well. I have never given a recommendation on which plugs to use...I'm just repeating what the others have stated over and over. I have learned from them and after using the NGKs, I never have to think about my spark plugs.
After reading your shaft rebuild thread in the transmission section, it is apparent that you are no 'dummy'.
Since you are a positive contributing member, I'd hope that some of the fellows would help you with your car, and I'm sure they will. You don't NEED their help, but if you are like me, you are willing to learn from others mistakes and thus save yourself a whole lot of grief.
So when I try to drive a point home, and suggest you use the cheapo NGK V-groove or whatever they call them these days, try to look at the positive side of it.
LONG time ago, (in Bethlehem) the boys were talking about their preferences for spark plugs on these particular engines. Several horror stories, and several recommendations were given for plugs. But let's not get to historical.
Rewind to 2010 and blueturbofly began a new thread on spark plugs. Here it is:viewtopic.php?f=32&t=46985
The one post I wanted to mention is by a fellow here 't3 ragtop' (also on GeoMetroForum) who is not 'THE expert' on the later model 1.0L engines like you own, but has a fairly good 'build thread' here:viewtopic.php?f=32&t=46400
He mentions in blueturbofly's thread:
ngk plugs, hands down. i use either the basic coppers or their u-groove plugs.
for a reason, and I believe it has to do with his personal experience.
I'm certainly no expert with engines and transmissions, having but little experience.
However, you do seem to be one of the more 'mechanically inclined' members on 'The Board'.
So I thought it would be nice to let you in on the 'inside track' of knowledge that the people who have been running considerable numbers
of these engines and what they recommend.
Again, I'm sure you're no dummy, and those plugs work great in a WIDE range of engines
. But check through the site and see what others have to say about them. Those who like them (initially) have engine failures if you follow their posts.
This is my observation from reading this forum over the past couple of years.
b.) Fuel Delivery -
If you look at the video I posted again, you will see an engine (3 cylinder) which has just gone through a fresh rebuild and is idling for the first few hours of its service life. Apologies as the carburetor is probably not warmed up enough for a 'warm idle', but you can get the idea of how smooth its cool (not cold) idle is.
The carburetor version engine is somewhat different than yours above the rings, but the basics are the same. Your engine, a 95 should be an 'improvement' over mine engine. I'm not sure, but I think I posted an '85 3 cylinder idling, and that was the FIRST automobile engine introduced by Suzuki to the USA. Make sure you look at the coil wire to get an idea of how smooth or rough it idles.
What is the point of posting the video? The carburetor version has a different fuel delivery system than your engine.
Yours has a TBI throttle body injection (as you know) so if MY engine with NGK spark plugs and a simple Hitachi carburetor that is somewhat a mystery to me can idle that smoothly, after ignition, you need to look a the fuel delivery. There is an injector in the throttle body and you can read Fainya's posts in Texas to see how he solved his TBI problem. Again, sorry for the long answer, but sometimes the 'short of it' misses its mark, plus you put a LOT of effort into the shaft rebuild thread and did an excellent job, saving cody, me and dattman the trouble, as we had all promised to do such a thread. Again, your fuel delivery could cause the vibrational issues you mention. And the 'short of it' would be to say that includes VACUUM LEAKS.
c.) Engine Internals-
Now, the last section that might cause you to complain about the vibrational issues of a 1.0 has to do with internals.
Whether it is compression related, or if there is some internal imbalance...these are the things which can cause an otherwise good fuel and ignition system to result in a vibrational engine.
Since you are adept and cylinder heads and blocks, there's no need to go deeply into that subject.
However, as tbirdscott mentioned (no I've never met him) you can balance your rotating assemblies at home with a minimal ($100 or less) investment in tools. Again, I'm not too experienced with engines and the like, and I've caught a LOT of flack from some people: "I'm oversimplifying" "It won't work" "It will make it worse" etc.
However, others who have tried it
seem to have similar results and so far no 'negative feedback'.
It is a simple man's technique and if you have access to a balance/blueprinter who will charge hundreds more, then by all means, go for it. One guy drove down here (Southern California) and watched/helped me balance the Wife's engine. I'll let you read what he had to say:viewtopic.php?p=334935#p334935
Here's the DIY Engine Balance thread:viewtopic.php?f=2&t=40445
Just like your transmission thread, the second time you split a case, I bet it only took you 20 minutes, so the DIY engine balance is similar. Once you get the hang of it, you can do the whole balance process in 15 minutes, as you only have to grind TWO rod caps.
As tbirdscott mentioned, our 3 cylinder engines are 1/2 a straight 6. And if you've ever balanced a straight 6 (like I've done with this method), you can stand a nickle on edge on the frame while the engine is idling
For fun, let's add
d.) engine mounts
Which is more to do with vibration being translated to the body, but it is something to consider.
Again, sorry for the long reply. You've helped a LOT of people with your trans rebuild thread, it's only fair we 'pay you back' by giving you the best information/experience we have to offer. You appear to be like most of us, no matter how little experience we have, we all enjoy the sound of an engine. I, for one, want your engine to idle like glass (unless you are installing a lopey cam) once you get it rebuilt and installed.