Same, I have a plasma and it works great, doesn't even know what HD ready means, but displays 1080i.
As long as HD is the max res the TV box gives, I don't see reason for an upgrade. (especially for a luxury item that is mostly background noice/movement)
My wife and I have one of each - a nice curved 55" Samsung something or other that does 4k, and a 42" Sharp Aquos LC-42D43U from like 2008 that's only 1366x768. But for what it is, the Sharp has amazing picture quality... And it weighs around 65lbs.