I have been seriously thinking about getting TI3:SE but cant decide.

What would you say would be the main reason I should pay out for it?

The new races are pretty cool. It also fixes some of the balance issues (in particular fighter swarms become a lot less intimidating). It introduces a few balance issues as well but overall I like it.

1) Far better strategy cards

2) More objectives rewarding aggression

3) Cool new systems with new abilities

4) Interesting new races

5) Racial technologies

6) More Action Cards and more importantly, more Political Cards

For those reasons, the expansion is an excellent investment. The first reason alone is enough for many people to say that the expansion is a MUST buy.

I second that. the expansion is an EXCELLENT investment. Don't delay, buy today!

Thirded to buy it. I rarely play with the original strategy cards. The new races are fun - you have the Muaat who start with a friggin Warsun, and you you get the Saar who have floating space docks. Yin and Winnu are fun too but not my personal favorites.

Also it includes enough tiles that you can play an epic eight player game which takes forever but is very much worth it