Personal opinion, seat tube angle and front suspension improvements over the years are no joke. Are your trails fast or slow and technical? Fast: modern bike because the wheelbase will be longer so the bike will feel safer and stable. Slow: the Intense should be good. For climbing, modern bike!! Having said that, I’m sure the Intense is a good bike but for the same money spent I’d go with a modern bike, even if it has worst components. You can upgrade components as it breaks/ worned out, but you can’t tweak a frame’s geometry.
Or, if possible ride them and see what YOU like. Either way, have fun
Also depends on how long you want your next purchase to last. Modern bikes have better options for upgrades and replacements in the next few years - depending on what that older bike was built with, the parts to fix the suspension or wheels etc may start to run out as well.
Another thing is servicing - 500 miles is either a few years of light riding or a season of hard riding, and either way that bike would probably need a checkover. Depending on work and availability, it'll eat up that $500 savings between the 2 bikes right away.
From personal experience - I was in the same boat. I used to ride a lot then took almost a 10 year break (moved, then kids, then finances/time...) and decided to buy a brand new "mid range" ($4000 Norco Sight A1) instead of an older "high-end". This bike rides better than the $8000 bikes I rode back in 2014 - it climbs better, descends better, fits better, and it's the bike I wished I had 10 years ago when I was in shape! I used to have a 2010 DH race bike and a 2013 trail bike and this one outperforms both together.