Checking them isn't as bad as you might think... but, you do have to be somewhat confident in your mechanical skills.. It always helps to find someone nearby that has done it before.
The plastic is nothing really.. once you get into that the first time you'll see how it all goes together and not as bad as it looks.
Having to actually adjust them ups the skill level just a bit and the right rear cylinder can be a hassle I've heard but have never tackled that one. I've helped with maybe 5-8 valve checks not including a couple I've done on my previous ST and only one needed adjustment.. but, that means nothing, you should check to at least have a baseline where the gaps are NOW... then, on the 2nd check you can see if those gaps have changed and how much... odds are, you are okay now but that's no guarantee..
I would check them now while you're not riding...
And, no matter how bad the ST is... it's nothing compared to how 'interesting' the Super Tenere is to do a valve check/adjustment.