Advice - temp trade what bores you now for something you'd like time with. When you get it back you can decide better how you feel about it.

As for what gets old - anything over time. I really only partly miss a couple of the games I've sold - Incredible Hulk (GTB Sys 1) and ... well maybe Centaur though it isn't worth the going price to me. I'd take two other Bally/Stern/Wms from that era for the same price. I'm hoping to get my Farfalla working soon so that covers that era. I'd love one EM and one newer Stern (IM, ST). Personally, and I can see many others are in a similar boat, I like variety of era, layout, rules. Some days I'll play through every game I own one at a time, others I'll start playing one game and just can't pull myself away from doing better on that game. I temp-traded Flash Gordon for Atlantis (GTB EM) for several weeks and it was a great trade. I have no intentions of selling my FG but trading was cool, give it a try.

As for lack of innovation, I'm less interested in fancy displays that I rarely look at than new playfield layouts and features or even just good adaptations. If any manufacturer was putting out great art on a single level deck with great rules and addictive challenging play without the added unnecessary expense of r&d just for bling...