Cass,
Like you, I replaced my drum machine with a keyboard, but it didn't solve the problem. The band members were still complaining. The reason they complained, however, was because they couldn't keep time worth a damned! They, like many others who play an occasional weekend job, could not keep time with a strictly regimented beat. So, when I purchased my first keyboard there was no difference--they couldn't keep time with it as well. When I purchased the next keyboard, a Yamaha PSR-500, I replaced the lead guitar player, the bass player, the rhythm guitar player and the problem was solved. I can keep time just fine with the keyboard, don't need to split the proceeds with anyone and I only have to worry about one person showing up on time--ME!
So, to answer your initial question "Do I need an arranger?" Well, the simple answer is yes, unless you have the burning desire to hire a drummer, bass player, lead guitar player, rhythm guitar player, haul a ton of gear around, spend an hour setting up and tearing down, put up with guys who can't agree on volume levels, timing, song selection, etc... NAH! Stick with the arranger keyboard. Which keyboard you select depends upon your individual needs and those of your audiences.
Merry Christmas Old Friend,
Gary

[This message has been edited by travlin'easy (edited 12-23-2009).]