I'm a big M&P22 Compact fan. I own a number (
cough, six, cough) of them, and I've found them to be the most reliable .22's I own. I use them as the "issue" pistol for NRA Basic Pistol, and for new shooters, so they see a lot of rounds. I say that only to establish that I've put in a fair amount of time behind the .22 Compact.
First, my guns go a long time between cleanings. My grandfather would be horrified, but there it is. And I shoot them suppressed a lot, so they get plenty dirty. I have found the guns pretty tolerant when it comes to getting dirty. Usually, I'll go up to about 1000 rounds before the get the ultrasonic treatment (depending on how much suppressed vs. unsupressed). I can honestly say I haven't had a gun go down due to lack of cleaning.
Second, if the adapter bothers you, I thing EWK Arms still sells the "barrel cap" to replace it. Yup. Just checked, and
they do. Really good people.
Third, I didn't feel the need to polish the feed ramp, but if yours has lots of tool marks, I guess a bit of
judicious polish can't hurt. Don't over do it.
Fourth, and I'm sorry to put this so bluntly, but I wouldn't piss on Thunderbolt .22LR if it was on fire. I run Federal Champion Bulk-Pak (525 Blue or 550 Maroon box) or CCI Mini-mags exclusively. I find I can eliminate many of life's problems by not shooting ****ty ammo, and my experience is Remington Thunderbolt .22LR is some ****ty ammo. Take that for what it's worth.
Finally, on accuracy, every gun is different, I suppose, and I read about some early .22 Compacts that had some leading problems, but I find the gun plenty accurate for my needs. This is a timely subject, because I just had #5 out yesterday for a quick checkout after it's long-overdue ultrasonic bath. This is 20 rds, off-hand, just outside 13 yards (odd number, but that's our range for you). Nothing formal, just checking POA/POI. It ain't a Hammerli Free Pistol, but this level of accuracy gets it done for anything I need.
Let me know if there's anything specific I can help with. As you can tell, I'm a fan of the platform.