I've invested a lot of money in this game and I still enjoy it. I joined late myself into a server of spenders, once I caught up in levels there really wasn't any big difference between me and the other spenders aside from who paid for what.

At this point I couldn't tell you what server would fit you best, but, assuming you want to spend a few thousand dollars, expect atleast 3-4 months of catching up on general EXP stuff. If a server has multiple people over 70k bp, it's likely highely competitive for spending.

Anyhow, it's a fun game to play but as some people said be careful how you spend early on - there are a lot of traps (ninjas) that will initially entice you until you learn they are free later or useless altogether. Try to avoid the "I can make this team/ninja work if I'm clever enough" mentality before you know a lot about game mechanics and such.