Do Blissey bases on OR/AS its much nicer than elite 4 runs and you're not locked in to completing the whole lot.
*kinda ranty*
To be honest, I prefer doing E-4 runs in ORAS. I put my Mega-Rayquaza in the front and 5 random pokemon to grind up and just run through it. When my pokemon hits its evolution level, I switch it to the front and let it faint. It'll still evolve, but it just won't get anymore unnecessary experience. If all my pokemon have evolved, I can just end it easily as Mega Rayquaza has low enough defenses to be fainted pretty easily. If I faint, I just end up back at the league, and can go straight back in without having to fly to another location.
Sure, I can do all of those things with Blissey bases, but paradoxically, they give too much experience. I like my pokemon to stay at their evolved levels, e.g./ Kadabras at Lvl16 or Feraligatrs at Lvl30. The E-4 gives enough experience to get there, but not too much to overshoot it. Meanwhile if I go to a Blissey-base, I could potentially, especially for a low-level pokemon, overshoot the evolution level by 5-10 levels, maybe even more. Also they're spread out, as secret bases are all over the place. They're also not infinite, though there's so much experience that you probably don't need to go to every Blissey Base, I'm just gonna go to the E-4 afterwards anyway, so why not just be there all the time?
Also, I just like going through the E-4 with Mega-Ray. Destroying every pokemon with a 1HKO is pretty satisfying. It's also less bland then blisseys over and over again, I guess.
*end kind ranty thing*
Anyway, I think I'm pretty much done with my Platinum Dex; The only pokemon I had left were Munchlax and Snorlax, because Honey Trees, but I gave in and just transferred a Snorlax from Leaf Green. I might go back and do some more honey trees, but for now, it's good enough for me.