WN2000RPTv2 only does 26 kB/s

26 KB/s seems really low.  It's possible that radio interference has increased over the years.  Your neighbors may have deployed their own Wi-Fi networks.  Baby monitors and certain cordless telephones also interfere with Wi-Fi.  

I would first try changing the Wi-Fi channel used by your extender and/or main router.  There are loads of tools that can help you survey your area for the best Wi-Fi channel to use.  Macbooks have built-in tools (option click the Wi-Fi icon).  Windows has free tools like vistumbler.net and Acrylic Wi-Fi.  iOS has a free Wi-Fi scanner in their Airport Utility.  Android, I'm sure, has something, too.

Try moving the extender closer to the router.

If these don't help much, then a newer model may help.  If your router supports 5 GHz, then a dual-band extender can make a big difference.  While 5 GHz has less range, it is generally much less used by people, so it may be a way to escape a crowded, 2.4 GHz spectrum.