The only experience I have with a record clamp is when I owned a Music Hall MMF5. I tried with and without, and although with a clamp warped records were a bit tamed, a better pressing made more of a difference. Bad pressings sounded bad regardless of any kind of weights. IMHO it's better to purchase higher quality records than spend money on a clamp. There are a ton of excellent 180 gram records out there. If you are dissatisfied with the sound on good vinyl you might want want to look at your cart before a clamp. Just my opinion.
I've never really stepped into the true HIFI of record players, so I really don't know what the differences are in the world of those who spend tens of thousands on a player. In the mid fi world I know the difference is minuscule at best.