If you are a graphic artist, a Postscript enabled RIP will print vector graphics better, print type better, and if you are doing production work, you can gang different jobs together on a roll easier. Since this is a sheet-fed only printer, the production efficiency advantages are greatly reduced if you want a RIP for that purpose.
In the old days, print quality may have had a slight improvement printed via RIPs, as RIP software used thier own proprietory dithering methods, but as stated earlier, the drivers Epson now has for these wide format printers produces superb dithering patterns, and may be indistinguishable from those from even the most expensive RIP software.
Thanks again John. You not only saved me some money, but you confirmed my suspicion about RIP software. Appreciate it. -Bill