I was reading some other replies that suggested using something to close all tabs and bookmark them automatically and I had the same reluctance as you do because I also group up my tabs.

However, this makes me think: what if there was a tree-style-tab extension that let you convert a tree into a bookmark folder? Then I wouldn't feel bad at all about closing half or more of my tabs.

This could be optionally combined with some sort of bookmark/page archiving service so you can be extra-sure that content will be waiting for you if you ever decide to look at it later.