You don't have to be a wallet warrior to enjoy WOT
I've been playing WOT for about 18 months. It's quite a bit of fun...I have been in over 3,000 battles.
You don't have to be a wallet warrior to enjoy the game, but the higher tier (heavier, more powerful) tanks will be effectively out of reach. The tanks are divided in to 10 "tiers" and in random battles, you will typically see a spread of not more than 3 tiers in the battle.
For example, when you start out with Tier 1, a small, fast, lightly armored vehicle, you will typically play with other Tier 1 and Tier 2 vehicles, with some Tier 3 mixed in. You can easily play the first five tiers without spending any money.
What the money does is allow you to accumulate in-game cash and experience faster, which allows you to advance to higher tier tanks faster. The bonus is signifiicant; 50%. Thus, it will take you a lot longer to get to the higher tier tanks unless you use real money. That said, there is nothing different about the mechanics of the game at higher levels. The tanks are bigger, heavier and more powerful, but the opponents in the matches are also bigger, heavier and more powerful too, so they balance each other out. It may take 6 shots for a Tier 3 to kill another Tier 3 and it may take 6 shots for a Tier 9 to kill another Tier 9. You can play quite happily in the low-mid tiers (I do most of my playing in Tiers 2-7) and not spend a penny.
Money also allows you to purchase some "premium" tanks, available at many tiers, that are slightly better than the regular tanks, but not enough to tip the balance. Of the 30 or so tanks I've played, only once did I buy a premium and it's not my favorite.
The other thing you can do with in-game money is buy better ammunition or better fuel or repair kits and the like. Again, these all give 5% or 10% improvements to your vehicle, and in the end, don't really tip the balance. If you are a good player who plays as a team, thinks strategically, knows when to back down and when to advance, those are way, way more important to your performance and winning percentage than any small advantage you can get with in-game purchases.