Besides form factor, JBL headphones, enhanced remote, and ethernet port, what is the difference between the Streaming Stick+ and the Ultra in terms of video and audio quality? Do they have the same processor? Do they have the same performance?
The only differences beyond the ones you've cited are
Model SS+(3810) Ultra(4670) Memory 1GB 2GB SD card no yes Channel storage not listed 512MB
In addition, the Streaming Stick+ has its wifi receiver built into the USB power cord where it is supposed to enhance wifi performance up to 4x the range, whereas the Ultra's is inside the unit. In Roku's own product description it says the Ultra has "our best wireless", so go figure.
Roku Streaming Stick +, 3810X, Ser YH0059427035, wifi LivRm - Samsung UN55ES6100
Roku Streaming Stick, 3600X, Ser 5S56D8240827, wifi BedRm - JVC EM37T
Roku 3, 4200X, Ser 4124C7087583, wifi GstRm - Sanyo DP26640