I would disagree slightly with j51, as I think some other R&F civs are also fun and/or interesting, including the Cree and Korea.
All of the mechanics from R&F, to the extent relevant to GS, are in GS (in some cases, in modified forms), so if you want the minimum expense to be able to play the current game, you are fine.
You don't specify whether you have the vanilla DLC packs, but if you do find you enjoy the game and have any "completionist" tendencies (as, sadly, I tend to have), you can watch for a deep-discount sale and pick up R&F and any missing DLC on the cheap. This will allow you to pick up R&F and DLC-specific achievements (if those matter to you)