I can remember Bull posting some house rules for PC vamps that made them a lot like adepts, basically initiating their vampirism to gain power points towards new abilities (upgrading Regen, taking Mist Form, Thermo vision), but also adding some new ones (Claws, etc). It worked fairly well for 3rd ed. This was years and YEARS ago, mind you.
If you want a variant Vampire, remember that Infection often activates recessive genes, meaning sleeper Mages and Changeling traits may manifest at the time of Infection. Gaining new powers after that seems... risky to me. You'd start to have a Legacy of Kain kind of thing, or Diablerie from Vampire: The Masquerade. It's a fun notion, and if you want to house rule it, go for it, but I'd say that's definitely outside the existing canon. After all, it would mean Martin deVries should have the Fear ability of a Banshee, for example.
If you want a rules-worthy compromise, you could just have them specify spells or adept powers that match the legend they are going for. For something that is house-ruled, perhaps gain new powers akin to how a Free Spirit might. You might devote power points/Magic ranks towards new abilities instead, or create a new attribute to reflect Infection and limit available powers to those you deem appropriate.
For what it's worth, I've played a vampire for years, and have had several in and out of groups I've played with and run, along with shapeshifters and more. If you really play it out, and have a GM who understands how to play to the strengths and weaknesses of everyone in the group, you'll have no problems at all. Point in fact: The Mage Vampire of the group rarely pulls moves so dramatically bad@$$ as the Street Sam/Rigger, nor gets so many kills as the Weapons Specialist. It's all about players. As said above, if you trust the player, you can likely trust them with any character and rest easy they will help you tell an amazing story. If you don't trust them with the responsibility, don't allow it.
