A small knit-pick: not "joining Russia", but "re-joining Russia".
In the rest I agree with you: There are a lot of disregarded places in Russia that need investment and rebuilding.
Crimea, however is not in a danger of losing investments in the longer run. It's had a very important strategic position for Russia for the past 300 years, and it's not about to change. Add to that that it's one of the few affordable Southern seaside places (Sochi being the other one), where "normal people" can go to for a holiday. With a federative structure (as opposed to the centralised one of Ukraine), Crimea will see a much larger portion of its income staying on the peninsular. All this gives Crimea a bright future.