Better results can be had from PC but of course at the cost of fiddliness.
Reencoding is not necessary except to reduce storage size, again at the cost of fiddliness.
Upconverting is not aboot improving quality as such but rather reducing the degradation from blowing up the image beyond the limitations of the resolution. So, I would not put too much effort into messin' with lo-def for use on an HD display, especially a large-ish one which may already be stretching the limits of HD sources. In any case, any TV from the last decade or more which is at least "HD ready" prolly already sports good scaling. Upconverting DVD players were kind of the final gimmick to push hardware sales in a saturated, commoditized market.