This article should help you out a lot donks:
Samsung Galaxy S3 4G Version Includes Drastic Changes; Is it Still Worthy to Buy the Smartphone? - International Business Times
So, in short, double the RAM, comes pre-loaded with the latest Android OS (4.1 Jelly Bean: You don't have to wait on the older Galaxy S3 for the update to roll out in your country, which could take another month or so).
Higher battery consumption when in LTE range, but LTE anyway is a battery hog. This can be remedied though in the future with a minor software update. Galaxy S3 has one of the best batteries in the market right now anyway, so it won't be lagging behind other phones by that much.
IMO if you would be changing phones over the next two years anyway, and LTE is of no use to you, then there's no point. Effective global 4G LTE deployment is still quite not there yet. But if the cost difference is not much, and you want your handset to be future proof, then I'd say go for it.