I can definitely recommend Hellas and Elysium as they not only give you 2 new boards to play around with, each board comes with it's own unique Milestones and Awards which can add a bit of seasoning so to speak to spice your game up a bit. I'd say if you can manage to get your hands on one for around 10-15 bucks, and you play enough TM, it's worth the purchase.

I'll add to what other people have said and give a hearty recommendation for the board expansion. I really like the Elysium board and think it makes the whole expansion worth it. It really adds a lot to emphasize the area control aspect of the game. The new estate dealer and desert settler awards are ones that wouldn't work nearly as well on other boards as they add a lot to get players to fight over either the North or South side of the board or neither if someone else is able to fund the other awards first. The big tile placement bonuses that give 3 plants or 3 cards are also neat. Personally this is my favourite map with the original being a close second and the other map being a distant third. I don't think this expansion is as mandatory as prelude, but I would highly recommend it to anyone who enjoys the game over any of the other expansions.

Actually you get TR for raising venus marker

famous last words........ another prelude has come out with them hinting more expansions to come

What is the golden cord behind you?

Nice use of, "nice," there.