Vectors have a much higher potential rate of return, especially if you do not offer the same vectors for all-one-price subscription sales as you do on sites that pay you significantly more for them.

Have you already been approved for vectors and are submitting the first batches now? or are you still in the application process?

My ports are mostly photographs as well but I am a graphic designer (having designed county maps) so I have a few vector illustrations in my ports as well...

and on both IS and SS my best sellers are vectors, no doubt about it, make up an overwhelming proportion of my sales even with very few illustrations.

So... that's what I would do, concentrate on vector art... I wish I could, I'm a single mother right now trying to finance a move across the country, don't really have time to be drawing pictures when I could be designing a website for a lot faster cash flow!

Good luck and let us know what happens!