If you buy tickets through Universal, you can get their value applied to new tickets if you don't go on this trip. You won't lose the value, but you might have the funds tied up until you do take a trip in the future. If you buy them through a third party, you will need to go through the third party for any refunds or exchanges, which may be as easy or difficult as the company dictates. Depending on the difference in price between the third party and Universal, you might decide that the price difference is worth it for the peace of mind that you won't lose the value of the tickets.
The only real risk to waiting is that Universal might raise prices again. Since the prices were raised in April, it's unlikely, though not impossible, that they'll go up again between now and November. Again, you need to weigh the risk that you might pay more later vs the risk that you'll tie up money purchasing non-refundable tickets now.
Personally, I think the risk of another price hike is low enough to wait. If there were some kind of promotion going on now, that might push into the camp of buying now to lock in an additional benefit, but they all look like full-price ticket options at the moment.
Full disclosure: we just got back from a trip for Halloween Horror Nights, and I literally bought my Rush of Fear tickets online while sitting in the airplane waiting for boarding to be completed. So, yeah, consider my bias as you make your decision. On the flip side, I bought our APs in March for a trip in April because there was a promotion to get 15 months instead of 12, and I wanted to lock that in. April 1st, not only was the 15-month promotion gone, but prices went up $50 per AP, saving me $200 and gaining me 3 extra months.
