Ditto on carrying a backup rifle for rifle hunts. The way I look at it - I look forward to these hunts all year, and have a limited amount of time when I'm there. Equipment issues that take more time than a trip back to the truck are too much. Didn't Tony Trietch damage his primary Hoyt last year on one of his multi-hunt trips? Maybe he'll chime in....
In the field for my bow I carry serving thread and allen wrenches for key rest / sight parts. And a small-game tipped arrow so I can check I'm still sighted in.
In the truck - I've got pretty much everything except a draw board. Press, tools, spare sight, backup bow...
My backup bow is close, but not exact this year. As long as you have them both sighted in, and practice some with both, I think you're fine. Most economical option is to make your current bow your backup when you upgrade next, and sell your current backup if you have one.