With the current
HD DVD pricing, personally I think HD DVD can become a bridge for people who wants to experience hidef for the first time, until Blu-ray price become affordable.
So to answer the original question, I think it's not a bad idea to keep your HD DVD player and get cheap movies that worth keeping. Until you can afford a Blu-ray player you can still watch DVDs on the HD DVD player.
On the other hand, since there is practically no new HD DVD movies anymore, I would suggest that you carefully manage your investment in this format (and Blu-ray as well).