I have been down this road. This is advice from my past experience having a thin-bowl Ovation and then moving to a better acoustic guitar (A Larrivee).

If the acoustic you have is already pretty nice, then use it but have a local luthier install an L.R. Baggs iBeam system and couple it with the proper pre-amp. This will run less than $500 and will likely sound much nicer than trying get everything for under $500.

There are actually very few guitars designed from the ground up to be an 'electro-acoustic'. Most are dissatisfying from a sound quality standpoint. The 'thin' size does usually end up with a thin sound. Those that don't cost well over $500. You have to get into the over $1000 category for a nice Godin or something with significant engineering included.

Here's some links. IBeam active system (lets you add a magnetic soundhole pickup later for more 'electro-acoustic' sound variety)
http://www.lrbaggs.com/ibas/
coupled with an L.R. Baggs Para DI
http://www.lrbaggs.com/paradi.htm

Regarding bowl-backed acoustics: Yes, they are fumbly to play with sitting down - my experience.

Regarding buying black: You know that this means the manufacturer can hide poor quality wood with the paint - if not, that's one reason manufacturers paint guitars.

So many other factors to consider. The main one is that when you play the guitar it should make you smile and say "I would play this for hours". If you can't find that in under $500, then save your coffee money for a year and keep looking until you can say that.

Shape does matter - find a shape comfortable for you for all of the conditions that you'll be using it in. To me, dreadnaughts dig into my side too much while sitting. Jumbos sound glorious but the size can be a hassle.

I settled on what has become known as the 'auditorium' type of shape. This is the shape that Taylor guitars popularized with their Grand Concert line http://www.taylorguitars.com/guitars/features/shapes/grandconcert/ . Mine is not a Taylor, and the upper bout is a little larger than a Taylor auditorium shape, but it still has a pretty narrow waist between the bouts which makes it comfortable sitting or standing.

What is the guitar you currently have?

My Songs, photos, writing,etc.
My Sound Cloud