To add to what Andrew has said. I have a Garmin Legend and it does loose it's lock easy under dense forest coverage. Overall it has served me very well. I don't know if I would get caught up in being able to upload your old maps into the unit you are looking at. I use OziExplorer to mark the sites I want to check out as a waypoint. Personally I use a prefix for each 'catagory'. Like an old school named Valley school would be named svalley. A park named valley park would be pvalley. I do that mainly because of the limited amount of characters allowed in my GPS unit per waypoint. The only reason I might recommend a GPS that can accept uploads or MAPS is that you could upload maps and it could help you orient yourself in unfamiliar areas. My Legend has the main routes (included with unit) in it which do help you orient yourself. MapSource is an extra cost above the GPS unit and will cost you $60-80 on an auction site and $90-120 or so retail depending on the package you are looking at. Are you going to be look for sites from a car or walking ... or both??? I am asking because I use my GPS hooked to my laptop thru a NMEA protocol connection (internal to the GPS unit). Using this protocol I can use OziExplorer with old maps loaded and drive around in areas that I have the maps calibrated. It's pretty cool. I can also connect to other software and do the same thing. I also walk and use waypoint to find those sites.
-Bill
-Bill