The 2000 Sundancer is a classic while the 2005 saw some pretty significant design changes.
The hull on the 2005 has a wider beam and more V, which gives it a smoother ride in chop.
You'll also notice the interior layout is more modern, with a lot more light and a more open feel.
No common issue stands out in my memory as of the moment, but it's all about maintenance.
Check for soft spots on the deck, especially around the windshield and fittings.
Look at the exhaust manifolds and risers, and if they haven't been replaced in a while, that's a big ticket item.
Make sure all the electronics, especially the dash gauges, are working!
It's also a good idea to get the HIN and run a check on the boat's history if you can!
Sundancers are great boats, but a pre-purchase survey is always a good idea, even if it's a smaller boat.