Let's be honest from the start, a PC port of D1 ain't happening. That said, D1 is still fun as is and D2 hit the apex at Forsaken. Sure, if you're an fps snob D1 is "unplayable", but for us regular folk a solid 30 fps is perfectly fine.
All that said, here's a poll on D1 and D2. Would you buy a D1 and D2 ReSpace version? D1 stays as is and D2 keeps all content up through Forsaken.
All campaigns are replayable at any point. If you want that sweet special gear, you get it by playing that high end content.