The problem with this question is a lot of it is not gas vs diesel but a better chasse.
The one advantage to diesel is you generate power at lower RPM and with a turbo, it doesn't lose power with altitude...otherwise for the same HP to weight ratio it will do as well, you just have to wind up the RPM a bit more when hill climbing (not that it will hurt anything)
Where it gets messy is diesel pushers benefit from a higher end chasse and the engine in the rear moving noise away from the cockpit. In principal, you could achieve similar results with a gas pusher but most people upgrading to a pusher will also upgrade to diesel, so they don't make gas pushers. So while it's pretty much always associated with diesel engines, it's not really the diesel engine providing the benefit.
Now if you find an identical MH with only the fuel type as an option (and of similar HP), it really is limited to the lower RPM and turbo keeping power at altitude and I wouldn't feel it's worth much of a premium.
