The downside to 50 amps is that the most 50 amp pedestals you will find in most CG/RV parks is max. 20% which is the min. requirement of the NEC with the balance at 30 amps .And that is in the most recent 2014 edition. In the 2002 edition of the NEC, only 5% of the pedestals were required to be 50 amps. I haven't researched older editions, but we were in one large older CG last year that had no 50 amps anywhere. If you want to increase your chances of finding 50 amp pedestals, go to relatively newly built or renovated ones.
There may be some "higher end" CGs that have more 50 amp pedestals available, but as that would cost a lot more to build, I'd expect to see premium rates.
With so many MHs and other RVs around these days with 50 amps, the competition can be fierce for 50 amps. All the $$ you spent to have a 2nd AC can be for naught.
If it were me, I'd install a 20 amp power inlet and run the 2nd AC off the 20 amp recept. on a pedestal. Could even install a 20 amp SPDT switch to switch the AC between the 20 amp inlet and 50 amp service.
I've seen some expensive MHs with a 50/30 amp adapter and an extension cord running out a window to the 20 amp recept. on a pedestal.
If you buy an RV with 50 amps, the dealer is never gonna tell you that 50 amp pedestals can be in short supply in a CG.