There's actually a whole cottage industry that has grown up supplying unofficial military accessories that are compatible with Lego, but that Lego would never make because of its stated stance against depicting "modern" wars.
Here you can get Lego compatible garands, enfields, mp-40s, mauser C-96s etc. that are being used in those overpriced Brickmania models:
http://brickarms.com/Toys/Weapons.aspx
I actually still collect Lego now and then. You would be amazed at the number of adults who do, I imagine it dwarfs the toy soldier market. Lego generally appreciates in value faster than toy soldiers, once a set retires it can start fetching double the original price (I'm not in it for the scalping). But if you want to invest in a toy line purely to make money, Lego is a good bet.
The detail in the modern sets is amazing. Check out this building (retails for $200 CDN - once it retires, I shudder to think what it will go for on ebay):