Hi Chris... let me add my welcome, too.
FYI: A high percentage of Painter owners also use Photoshop (or Elements). These programs compliment each other.
While there is a great deal of functional overlap, as John indicated each has unique abilities.
For photo-art purposes the only major advantage of upgrading from Elements to Photoshop I can see would be the abilty to create
actions (recorded command scripts) that can come in handy.
That said, upgrading to
PS would not gain access to the Painter-only features, so given your situation I'd definitely opt. for Painter.
If by chance you are a student, have children or relatives who are students, etc. look into acquiring an "academic" version of Painter. Exact same functionality as the "standard" version, but considerably discounted price-wise. Another possibility is to look into the Painter Essentials program, a "Painter-Lite" if you will... a lot of Painter's functionality for about 1/3 of the price.
Before taking the leap, consider browsing the "Painter WOW!" book (for any version of the program) at your local library or bookstore. It will give you an idea of what's possible with the program.
Beware, too, that the more artistic skill/talent one has, the more one will be able to get out of either Painter or Essentials. Otherwise these programs are used, in essence, as creative digital tracing tools, which is how most people who are getting into "photo-art" these days use them. That's not necessarily bad because it's possible to create some very impressive art (by what's known as "cloning" and "autopainting"), but it's like buying a Ferrari and only driving it 10 MPH.
Good luck on your decision. Hope this helps. Let us know what you decide to do.
Also... click my name above/left and send me an e-mail. I'll get you going with the
Impressionist plugin, that will come in handy no matter what you decide.