Trade routes are a decent source of science if you're behind. You have double. All those science is going directly to your capital, which will have all of the science buildings and national wonders and presumably be really tall. So, you probably won't be tech leader, at least not until late game (if you go on a buying spree, then add some multipliers on your new-found science w/ RAs, for example), but you also won't be THAT far behind in tech. With the slow pace the AI builds/upgrades units, you'll probably be able to upgrade/buy yours (you have tons of gold) in time to not be behind military-wise.
Also, you acquire cities with more pop than cities you'd build, without having the penalties of happiness or having to buy/build a settler (which together, pretty much equals the value of a GP). I don't see a disadvantage here. You'll be able to get as many cities as you would otherwise. They'll actually be bigger than your cities (assuming you acquire them early-mid game) had you have to build them, and you get an indirect happiness bonus. The disability evens out with the ability in early/mid game. In late game, your ability to peacefully acquire cities with huge populations (and buy science buildings in them) is a huge asset.
That's just science victory, and probably the toughest one to pull off. Culture victory is an obvious one. Money buys great works, and you can pick CSs that have archeological sites to buy. Diplomacy is designed so that anyone can achieve it, and if you're picking your spots and staying out of the way (say, only buying CSs on island chains to maintain good diplo), you'll not only have enough money to ally CSs you don't take over, you'll also have enough gold to bribe civs and their delegates. Domination works the same way as any other domination game, only instead of extra production cities, you have extra gold to purchase those units.
It all looks pretty balanced to me.
I would be amazed if the AI uses this civ well though.