What should be a "perfectly viable race" is debatable. IMHO if something has a LA, it should be playable.
Even if you might like that, that is simply not the way it is. Some abilities, creatures, templates etc. tends to to be fun when a opponent has them but breaks the game when in the players hands. Dominate at will, the vampire spawn thingie and energy drain are abilities that can bend
some types of games out of order.
Therefore the Vampire must have a high ECL. If you and your DM then agrees that those abilities doesn't have much impact on
your game, by all means reduce the ECL to a value that you think will fit better.
In the rules they have to choose the ECL with the worst case scenarios in mind. For instance in my games the Vampires official ECL of +8 would be more or less spot on. I just know that several of my players would be able to get a lot of mileage out of the vampire abilities and some of them could completely wreck the game with a vampire pc.
Things like solars have no LA for a reason.
Thats easy. A solar casts spells as a 20th level cleric and surpasses a 20th level cleric in any possible way. Of course it should not be playable except for a epic game.
His Diplomacy, Gather Information, and all Knowledge skills will be eight ranks behind a standard-race character of the same ECL. I'm guessing that, if you're playing an urban based, socially plot-driven campaign, those skills will all be pretty critical, and the vampire won't be worth half a damn at any of them.
He will do fine with Bluff and Sense motive most of the time, dominted victims will tell him what he wants anyway. And even when he needs those other skills it will be the same as in any other group, if you need a character with a good gather information skills you arrange that one of the other characters does that. What the vampire's skill bonus means is that you can play a vampire fighter or monk (possibly the best classes for it) and still be pretty good at social stuff and sneaking. In effect you will end up being something aking to a rogue. Less than stellar combat ability, a nasty circumstantial special attack power (energy drain instead of sneak attack) and decent skills (but not as good as a true rogue)
The vampire will quickly find himself with the city guard and probably clerics and/or paladins from some of the local churches/temples hunting him.
And at this point he either uses his powers to flee and return a hundred years later when everybody has forgotten him. Or start making vampiric spawns out of commoners (of which the majority will die from just a touch of level drain) and let them run amok in the city (creating wights) while blackmailing the city powers to stop the clerics/paladins to end this menace to the population. (this actually happened in one of our games, just with the twist that the players where the ones hunting the vampire. In the end we had to give up, too many innoscents were killed, the cost to catch the vampire simply got to high).
IMO the main point is that the official ECL is not something that should be considered set in stone. If you (in theory or practise) finds that it is to high for your type of game change it.