Should You Get an Older Kenmore?
The answer is NO. In case you hadn't seen the discussion here on the forums, those machines, along with those sold my Frigidaire, Tappan, Magic-Chef and countless other manufacturers were produced by D&M (Design and Manufacture).
Ask any of the people who repair dishwashers on here (Combo52, SteveT, RedCarpetDrew and others, I'm sure) and they will re-iterate what I am about to say:
Based on what I've read here by reading archived threads, those older machines were some of the cheapest, most unreliable dishwashers that were ever produced.
The Porcelain tubs were so thin that any chip, bump or crack could cause enormous rusting issues, the heated drying vented through the unprotected metal door, allowing it to rust, the black sump cover was really designed to COVER UP rusting issues, the timers were unreliable. The list goes on.
Following the move to Plastic tubs, as you'll see in the thread linked at the end of this paragraph, those rusting issues were eliminated, but reliability was still questionable (Read onwards after Nate's report to see "testimonies" from others who had owned the machines). Sure, these machines and the ones preceding them could clean very well, given quality Phosphate detergents, Hot water and Rinse-Aid, but even the models with "Filters" and Food-Disposers were highly capable of evenly coating every dish with ground up bits of food. There was another thread (Imperial forum, many years ago) that discussed that didn't happen (A performance test of the Roto-Rack WITH heated drying), combined with good old fashioned Phosphate detergent (perhaps with Chlorine?) and plenty of Rinse-Aid to stop stuff sticking, you might be okay.
Machines of Ill Repute, Volume I - The Later D&M Kenmore:
http://www.automaticwasher.org/cgi-bin/TD/TD-VIEWTHREAD.cgi?37812
http://www.automaticwasher.org/cgi-bin/TD/TD-VIEWTHREAD.cgi?37812
Fellow member "Launderss" owns one of the later model Frigidaire (rebadged Kenmore, or vice-versa) 18" dishwashers of the older design of the thread linked. It seems that dishwasher is capable of working very well, given Hot water and additional STPP for Pre-Wash and Main-Wash phases. So you might have similar luck with an equivalent model (which is what I'd recommend if you went "vintage.")
Really, if you are going to go somewhat vintage, you might just want to consider a builders grade or BOL machine, like a Hotpoint or GE dishwasher before EnergyStar tightly coiled around the necks of our machines. These machines might use water, and whilst being cheap builders machines are still highly capable (Especially with 7 or 8 water changes!). The thread below gives an idea about something I would personally take if I was in your situation. Besides, these machines are far simpler than the Rapid-Advance, Rusty Porcelain Kenmore machine you want - Turn to Start, 2 cycles. How much more simple can you get? Thread attached is another Canadian's report on a builder-model "Beaumark" (GE Rebadge) dishwasher. Based on information from member "bwoods," I think that model would be a Potscrubber 640 - A select model that included the Self-Cleaning Filter, but was essentially just a Potscrubber 600.
http://www.automaticwasher.org/cgi-bin/TD/TD-VIEWTHREAD.cgi?40536