This depends a lot on your status situation and the availability on the specific flight:

1. If you're like me and usually squeak by on EQM for EXP, and if there's C open at booking, absolutely, love this strategy.

2. If you're the same flyer as above but there's no C available, you have to ask yourself whether you'll be any more likely to get the upgrade than you would just relying on your EXP complimentary upgrade.

3. If you're lower status you have to wonder whether you'll clear it at all fighting the EXPs.

4. If you either a)have no status and don't intend to get it or b)easily clear EXP targets, then there's no point to paying just to get the EQM.

I don't know where OP falls on these scales. But it's definitely a suggestion worth thinking about in the right circumstances...