I completely understand and have been there myself and have learned the hard way and more expensive way. Just wanted to offer some other thinking for you to consider. However, I think you'll be surprised at how much difference the wheels themselves will make. You can postpone a bike upgrade for even longer by just spending more than what you'd budgeted. When it does come time to to upgrade your frame, you can then spend less overall because you don't need another set of wheels. Should you buy the Mavic's today, and I agree they are a good value, you'll be okay with them for a while, but at some point you'll want to go to the next step. I'm just encouraging you to think about spending $200 more and going ahead to the next step now and save yourself the $300 in the long run. Of course if you're working under a really tight budget and all you have available is $300 then any thoughts of an additional upgrade is really a moot point.

However I should add, a lot depends on the type of riding that you do or plan to do. If the terrain is pretty flat and you're doing lots of solo riidng, the Mavics are as good a choice as any. You really shouldn't worry too much to try and get to a lighter weight wheel. The biggest advantage of lighter weight wheels are hills and riding in groups and needing to accelerate, close gaps or bridge up to other groups.

Whichever route you go you will be very pleased with the upgrade in wheels. It's the biggest single change you can make to a bike to enhance the ride.