I've stored wine in the 60s for years w no problems. Do you KNOW how warm your basement gets? Figuring about 60 isn't the same as actually knowing. I've taken measurements in mine for years and while I think it's in the 60s, it actually gets into the 70s once in a while.
If you really have lower temps, and you insulate the ceiling especially, since your top floor is no doubt going to be heated, maybe you'll be OK minus the flooding, etc., as mentioned. But for only $1000 a year, I might store it off site.
The thing is, the wine will age differently than if it's stored in the 50s. Doesn't mean that's necessarily all bad, but it's not going to be the same wine. If you've ever tasted side by side bottles stored in the 50s and those stored in fluctuating temps, you'll see the differences very quickly. Things like brett and any bacteria problems develop much faster at higher temps for example, and slow polymerization of tannins isn't as fast as some of the other reactions, so you get a different texture in the wine too. But again, I've done it and the wines have been fine.