Unfortunately, there are no easy answers for you.

How much are you saving by using Priceline versus Expedia? Is that money you can save and use on a future vacation? Lets say you are saving $20/night using Priceline and you stay on average 50 nights per year. That would mean you could be saving $1000/year. Assuming you used Expedia and you paid $150/night (and you are a Gold elite using the Premier Marriott Visa card) you would be making about 135K points per year plus throw in a few bonus points for promos like the Megabonus (we'll say around 50K/year). That gives you a grand total of about 185K points/year. (Given a few more promos, use of CC on non-Marriott stays, etc, you might be able rack up some more points.)

Two items of thought here:

1. You now have Gold status as you are getting credit for your stays. If you are staying at FS Marriotts, this would mean CL access and free breakfast. That might save you some money as well. (How much do you currently spend on breakfast during your trips?)

2. You should have enough points for a Standard 7-night award at even a Cat. 7 hotel, which means you could stay at places where it would cost significantly more than the $1000 you saved.

Now you can play with your nights, savings, hotel costs, etc and decide if the savings is worth more to you than the cost of the awards.