I agree. I use my 3600 every time I travel, and it works just fine. In fact, it works better (more powerful, less delay when pressing buttons) than the small Insignia Roku TV I have that's at least a year newer. Unless you need 4K support, or feel that the reported improved wireless radio is worth the update, there's no other compelling reason I can think of to update. . All Sticks, including yours and the latest versions, support 5 GHz wireless, so that in itself is not a reason to update. The new Sticks support 802.11AC, and the remote includes voice search. That and a faster quad core processor are the significant changes from the 3600.
Dan Roku Stick (3600), Ultra (4640), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.