I think the Indians are an above average civ, possibly in the top ten. I think that the fast worker is an above average UU. I've played as the Indians for at least 50 games, usually on normal or marathon speed. Based on that experience, some points:
IMO the Indian fast worker is the best UU in the game. You get their ability from the first build until the end of the game with no upgrading. You get hree MPs which means they get to their target earlier and can start building immediately instead of waiting the next turns. Also captured workers can speed to your hme territory real fast.
That's an illusory benefit. It's definitely nice in the early game, but workers have a few basic phases in civ4:
-- Capitol development, where you just work on the next tile your city will be exploiting. Fast workers are marginally helpful, since they can get their faster.
-- Expansion, where your need for improved tiles may exceed your supply of workers. This is where FW's shine.
-- Conquering. After you conquer enemy territory, you may need to change its tiles to suit your strategy. The FW is of marginal benefit here; your conversion of enemy land will happen faster, but only a few turns faster. And when you kill an enemy civ, you're likely to get all his workers, and will have more than enough manpower to reshape the land to your will. [The only exception is when workers are outside the enemy's last city when you destroy it; unless you require complete kills, they just vanish.]. So... of help here, but not that much.
-- Building a railroad network is a huge project, and greatly reduces the amount of garrisoned troops you need to defend the homefront. But the UW isn't really useful here; the limiting factor is the time it takes to add rail to a tile, not the amount it takes to move. After all, you can start building your rail network at any point. And it's not like discovering the railroad comes as a surprise; you have plenty of time to reposition your workers appropriately. So, marginal benefit.
-- Once your rail network is built, you only have post-conquering to really worry about. You'll occasionally need to change a tile or two, but even regular workers can get about quickly on your trains. So, the FW will only be marginally better once again.
-- Therefore, past the age of rail, this UU isn't that great. So, saying you get the benefits of it the entire game is kind of false.
So... it's a good unit, especially in the early to mid game. But superior to prats? I tend not to think so.
Let's also consider the Indian UB. The mausoleum's +2 happiness is good; the cities where its benefits come in most handy is where you'd build a jail anyway. On the other hand, you can't build it any earlier (like you can with the Sumerian Zig), nor do you get any discount on hammers (IIRC; I'm on the road and don't have access to the civopedia). As I said in the start, the Indians are above average but not a truly elite civ.
YMMV.