Yeah, this idea in general is not worth it. It's too costly, and for too little gain. Disabling their buildings is only really useful if you have stuff nearby to take advantage of that. The pretty much means early game this is useless. Plus the time for that one convec to get over there would slow down your growth too much.
Also, if you want to detonate it right away, you'll need some kind of combat unit nearby, and probably something like a starflare too, which means you'd lose the convec building it, the starflare, and the tokamak too. If you let it finish building, then it'll take more firepower to kill it (although you don't have to lose a convec). You still lose out on the time though, where that convec could be building other things.
I'd also like to state that losing a power plant (permanently) early in the game is much more harmful to you, then temporarily disabling a few enemy buildings.