welcome back, mike, to cfc! It took quite a while for you to do your first post.
Look, you still can play gotm with 'vanilla' civ3. There are a lot of players who don't have any alternative, the mac players. therefore, 'vanilla' civ is by no means outdated.
But GotM - or 'Classic GotM', so it is called to distinguish from the c3c COTM competition - has gone a long way from the initial incentive. Since GotM 17 the games are modded to meet the PTW version. The add-ons are in sum quite big, so if you want to take it, there's a bunch of downloads waiting for you.

On the other hand, with this stuff you can upgrade your Vanilla Civ3 to be like (almost) PTW. You get new Civs (Spain, Ottomans, Vikings, Koreans ...) toegether with new units and such.
If you want an overview, have a look at
the GotM reference thread. The essence is, you need the add-ons for GotM 21 to GotM 25 to play GotMs since GotM 17.
In case you have a MAC, please have a look at
Alan's thread.
What do you think?