You could do evolution sets, starting from what you envision the egg to look like, the baby version (if applicable) then stage 1 to stage "x". Or even do battle scenes between two pokemon that could be on even footing. Everyone and their mother does pokemon posing for something, but very rarely do I see an actual action scene.
For me, I grew up with the first 150, the additional 100 were cool, but I stopped caring past that point. A large portion of people my age that I know are also like that, and we are people with jobs and have (or are starting to have) some disposable income.
Still the things that I've noticed that may increase the demand are: 1) Background story from TV/Comics/Movies, if you don't know em why should you like em? 2) BA factor, mo powa mo betta 3) Fluf, and lots of it! 4) Nostalgia, bring back the good ol' times
I know there are plenty of other factors as well, some more subtle than the others. If you want some place to start, go see what is popular right now and think, "how could I make that better?" or "what could be done to make me want to buy this?"
Most of the Dog pokemon I like but two of my favorite are Gyarados and Blastoise. Some others I liked were Lickitung, Scyther, Lapras, Houndoom, Donphan, Jirachi, Raikou Entei and Suicune. Lol I don't know many more that those since I stopped playing the games after Pearl.