While Catty & Vire both add something good I've found that in games I've played the effort to set up a Delcatty or Buzz/Vire ends up slowing down my early game a bit. Skitty, Buzz, & Kid starts are not what you want either.
Delcatty energy draw & EX upstream do add useful stuff to the deck but make you a lot more power dependant for setup. An early opposing CC can hurt you more than a pure Blissey deck with it's more robust trainers. Those Catties are also pretty vulnerable.
Vire adds a heavy hitter and Vire level X is fantasic for getting rid of bad tools & stadiums ... but having to invest so much in Lightning energy really hurts since Holon FF & Holon WP work so nicely with other Blissey builds. You loose a LOT when you give those up.
In both cases Mono fighting weakness isn't all that great.
After DP3 I suspect that Bliss9 (Blissey + Arcanine) will be about as good a solo Blissey.
Blissey center is nice too...*with sceppy and ssu*. But its really metagame dependent. If you have the space for plus powers and charms, then vire is such an amazing card in the format.
Currently Im playing solo blissey and it worked nicely. There's some flaws though - that is u dont have alternate attacker, and no delcatty slows the deck a bit.
VireIss can alternate attackers. Blissey is better early to do damage fast and get more energy into play. Then it's time for a Vire to attack for a bit ... then it's likely that you will attack with a Blissey to get energy out of the discard. Once more energy is back in play it's back to Vire. Of course the game state will also change things a bit.
The problem about Blissnine in US/EU compared to Japan is that Japan got Briney to save damaged Blisseys/Arcanines. We have to rely on SScoop Up, which is too luck reliant to be reliable. Japan can also Stump away too damaged Arcy's/Blisseys.
Well, eventually, Arcy/Blissey might become popular, but Empario KILLS it... but I don't expect THAT to be played excessively.
One thing I don't like about plain Bliss, is that you donj't have any alternate ways of attacking... so Vire can help with that, and Catty (played 3-2-1 in my opinion) can help with speed.
Blissvire, if used correctly, is probably better because of it's speed and huge damage potential. But if Mario is huge in your area, go Blisscatty since you can get rid of the weakness with FF.