Hello Mark, welcome to the forum!
It doesn't really make sense to upgrade the output of your DVD player to a higher image resolution, if the TV set cannot display that. However, even on a 480 fps TV the picture will be better already, because of the visible improvement of the horizontal resolution.
So, the most important questions are: what is the (max) physical image resolution of your TV set (how many pixels on the screen), and does it have an HDMI connector?
If the TV you're not willing to replace (yet) cannot display HD images, and if your current DVD-player really has to be replaced, a more logical choice would be a Blu-ray player. The image would be as good at least as that of an upgrading DVD player (it up-scales DVD images as well!), you can start enjoying and/or collecting blu-ray discs if you want, and you're set for a future upgrade of your display.
If your TV set can display HD images, that solution makes even more sense, and with the prices of BD-players coming down as much as they do currently, you may find it an interesting option to consider. Up-scaling DVD-players are now simply one notch below a BD-player, technically speaking.
Apart from the (important) ability to play Blu-ray discs, the whole consideration of adding an up-scaling DVD-player to your setup is technically the same as that of adding a BD-player.
Hope this helps.
Cees