Thanks for the information, Norm and Tim. It was very helpful. Just wanted to post a followup.
I'm glad I waited to purchase because all of a sudden the Thalys fare I wanted went to 1/2 price - $60. I had seen mention on raileurope that there was a 1/2 price summer sale until 9/30 but everytime I searched all fares came up as $120. I guess they finally put it into effect for the day I wanted, which is actually Sunday 9/30, so I'm in luck!
Also the TGV to Paris CDG on 9/30 AM went up to $86/$72 so that wasn't looking good anymore.
I did investigate the Smilys rountrip fare on sncf and that looked great and I was about to do that. But that is good to know for the future anyway, I never heard of that one before.
I really didn't want to pay $120 for Thalys when I'm only paying $94 Eurostar from London to Brussels.
Btw for anyone reading this that's interested I see many days in September that have $60 one way fares on Thalys so take advantage of it.