Well the gold opens doors for a while, but you'll reach a point where there's nothing you can purchase which is an upgrade.
It will be nice to be able to buy epic flyers for your friends when they go Worgen/Goblins in Cataclysm, or to do the same for your entire team as soon as they qualify.

Similarly, BoE's which drop in 25 man raids that you cannot box, are more immediately available.

On my server, there are very geared pvp toons who will group with your toon for "x" amount of gold in a 2's arena team to get your rating to whatever. Generally they charge so much for as many games as it takes for you to reach 1800, which gets you (I think) the lower end arena weapons.

Some of the better geared guilds, which have everything on farm have introduced GDKP raids. You basically get 8 or 10 people who want to gear up, with the rest of the raid able to essentially solo the content. They try to have 2-3 people able to use each type of drop. And then something drops, you bid against the others, actually paying 25x whatever you bid. After the raid, the total amount is split 25 ways, which can be decent when gear goes for 5k or 10k per piece.

Gold opens options like these.

But, you reach a point where its only purpose is the game of how much can I get in total, or how much can I make in this time period. Or can I control this entire product on the auction house.

I'd like enough to basically do all of the above, and to not ever need to farm it again. I'll probably do the transmutes faithfully, for quite a while even when I don't need the gold. But, it is a means to an end, and not the end purpose, at least for me.