The BTS bombing, whilst terrible - wasn't anywhere near Ari station. The reason that Sala Daeng station was hit is that it was within firing range of Lumpini Park (where the red camp was) - there has been no trouble on any other part of the lines
Supposedly on the 15th, the Red Shirt leaders will be surrendering, but this of course could all be a bluff...
Maybe hold off for a week and see what happens?
p.s. I know it's very easy for me to say "don't worry!", but then I have been here on and off for 2 years so am used to how things go down. For someone who has never been to Thailand before, I can certainly understand your apprehension - I would probably cancel myself in the same situation.
If you do decide to make the trip though and need any help, please let me know. Alas I won't be here in 6 weeks time, but if there's anything I can look up for you beforehand, I'm happy to do it.