I have both a 22.5 and the 26.75, and while it doesn't sound much larger, in person it feels like double the size. I wanted a grill/indirect cooker when I bought mine because of the extra indirect room on it. You can smoke the largest packer briskets on it with ease. If you use the grill space occasionally, I would go for it. I wish it didn't cost double the 22.5" OTG though.
Traeger Texas, UDSx2, Weber 22.5" OTS, Weber 26.5" OTG, Weber Performer Platinum Blue