Frankly Im a bit surprised at some of the posts I have been reading......... a street 500 would be perfect for a new rider.
Its a "Harley" so you don't want to drop it.......... well no kidding, but I promise you that you don't "want" to drop anything. Word to the wise, its not if you drop a bike its when, and it doesn't matter what name brand is on the tank.
As far as the power goes, do what feels right to you....... but take it from someone that has gone through the motions, if you buy small there are very very good chances you will want to upgrade quickly. Especially if you ride with someone who has a bigger bike and you want to keep up.
If you are thinking street, do yourself a favor and spend the extra grand to get the 750. The "power" is all in your throttle hand, if you can control your own body you can control the "power". You can ride a 750 like a 500 but you will never be able to ride a 500 like a 750 (without a trade in or engine work anyhow)
As far as the V-Rod comment, I beg to differ; but if I may my 08 VRSCD (Night Rod) is a mid control bike and you can put mids on most any Rod right out of the H-D parts book.
Now with all that being said, if you can get a Honda 250 rebel real cheap ($1000 or less) and want to learn on something like that go for it, you will always be able to get most of your money back if not all, but don't go spending $4000 on something else when you can get a street for $5000 (close to it you know what I mean) and if your going to spend anyhow, get the 750 so your not getting left behind when you grow up on the bike and at first ride it at your skill level.
Sorry, rant over. Just keep in mind, unless you have limitless money choose wisely, you may just be stuck with what you buy. Might as well make it something you want to ride for a while.