I have replaced a seam on a used tank & it wasn't difficult at all. I would give it a try as long as you can get the glass at a half decent price. The small side piece is much easier to work with than the big front piece ... plus, the cost of the front glass is such that it may be cheaper to buy new.
Just make sure you get the right thickness (tempered glass for most new tanks), & have it cut to exactly the right size ... should be within 1/8 inch or better.
80 gal FW with 30 gal DIY wet/dry/sump.
9 fancy golds, 1 hillstream loaches, 1 rubber-lip pleco (C. thomasi), 3 SAEs, small school of white cloud minnows, planted.