If you are interested in playing it, then by all means, keep it and buy some more games for it. If you don't think you'll play it, then it's possible someone on the forums might be interested in buying it from you, if the price is reasonable.
As far as modding it, that's really a personal choice. Some of the better mods will give you amazing picture quality, but the cheap mods are really hit and miss. The best mod of the money is the UAV. It will give you great picture quality and it's not expensive. If you can solder, it's not hard to do the mod yourself. Just steer clear of the mods that you find on eBay. If you can't solder, then there may be members near you who will mod the system for a fee. Honestly, if you are getting a decent picture with the RF, you don't need to mod it.
Also, if you are going to keep it, don't overpay for games. Common carts are super cheap and easy to find. Read everything you can on the forums and feel free to ask questions if you need to.
Post some pics of your 2600!