We went to the Surin Elephant Festival last year. I would recommend that if you go, only spend 2 nights, (1 full day). We spent 3 nights there which was one night too long. There is nothing to do in Surin once you have been to the festival show. Given that information, I did think it was worth it. We took the train from Bangkok to Surin and back to Bangkok again. The scenery from the train was memorable in itself. It is a 6 hour train ride which you should do in 1st or 2nd class. Definitely do not travel by 3rd class.

Picadilly, thank you for the reply. A couple of follow up questions:
1) Where did you stay in Surin?
2) I remember reading somewhere that the same program is presented on both Saturday and Sunday and that on each of the two days the show is three hours long and is over by noon. Is that true?
I'm very interested in your reply. Thanks in advance.

I was also in Surin last year for the festival but was living in a nearby town so did not spend the night there. One day at the festival was enough for me. The market that sets up near the festival grounds was interesting but everything was priced for tourists and the vendors were not willing to bargain. I disagree that there's nothing to do in Surin - there are craft villages nearby for both silk, baskets, and silver if you are adventurous and willing to get off the beaten track. If you are looking for nightlife, then perhaps Surin is not the place for you, but it's one of my favorite small towns in the country. Even though I never stayed there, I am told that Pirom's Place (66-44-515140) is the place to stay. Pirom can suggest ideas for day trips around Surin including excursions to lesser-known Khmer temple sites. The silk in Surin is some of the best in the country. Since you mentioned the time constraints, there is an overnight train from Bangkok that gets you into Surin early in the a.m. (around dawn). First class sleeper cars are around US$20 (there was a rate hike earlier this year, so I'm not sure of the exact fare) and are comfortable - and a wonderful way to travel. Bring your own snacks on board. The food service offered in first class is awful. I enjoy 3rd class travel for the food vendors, but it's not a comfortable way to travel. Flying to Surin is also an option. The price is very reasonably (US $50 or so last time I checked), but the airport is about an hour out of town - so the train was always our preferred method of travel. Hope you have a great trip - SAWATDEE KA!