To be honest, if you come in saying you want high quality themes, but aren't worried about money and it is mainly for your portfolio. Your motivation might be in the right place, but in my opinion it probably ends there. And having the right motivation I think is not enough to actually create high quality themes. Not in the long run.
If you make two to five themes that look pretty on the outside, and a few people use them. And a portfolio is bigger. I can't help but ask myself "But, if I were to hire this guy based on his portfolio, how high quality are these really?".
And sorry if it offenses you as I can't get around the fact this can be viewed as being targetted personally against you by me saying this all, but placing a statement like that, when you're asking a question with the argument 'high quality'. I don't see the trust - which should come with 'high quality'. Maybe not on paper, technically the customer has nothing to do with trust when they use a theme. But a freelancer has a portfolio for a reason, and that means the direct marketing step of 'repeat customers, build long term relationship, get a revenue stream going' is a specific decision. And then trust comes into play. Your visitors will see right through that, especially after paying once.
Is there a market for high quality themes? Yes, but I believe only for high quality themes. Anything less is something the user can easily do (with the three points I mentioned in the first response). But it's only high quality if it is .. high quality. Self-aclaimed high quality where it's only feeding a personal portfolio .. I personally do not consider that high quality.