Hi Steve, I'm in NM, and familiar with Swamp Coolers, and work on them all the time. Gotten pretty good at it actually.
As far as synthetic panels versus Aspen Straw panels, I myself really like the Synthetic Blue stuff the best myself. they claim better cooling with most synthetic Panels, but in all actuality, there's probably not a heck of a lot of difference.
The downside with Aspen Panels is the tons of Straw Crud that always accumilates in the bottom of the resovoir, and if the Water Pump Clogs up, then it can't do it's job of Pumping, and Spraying Water onto the Panels. I've seen this stuff clog up the entire system from the pump, and particularly the Spray Bar-Spider.
The old Round Swamp coolers can really be a headache, with the round PVC Spray Bar, that has numerous little holes drilled into it.
The Spray Bar must provide full flow for the Swamp cooler to work it's best.
Soft Water versus regular Hard Water? Well I'm sure the soft water has to be a improvement versus the hard, as the PH probably isn't as alkalinic with soft water, and thus there will be less build-up of deposits. Water in NM is generally loaded with Caliche, and the only thing I use local water supply here for is Bathing, Brushing my Teeth, the Swamp Cooler, and the garden-lawn.
Having fresh water flow in constantly I suppose could be an advantage, but here in NM, generally during the day with high heat, there's plenty of evaporation taking place anyway within the swamp cooler, and the float is usually always-a-trickling.
I find that here, one cannot go an entire season without periodic service, draining of the resovoir, and using a cleaner-conditioner, and once flushed, I then use an anit-bacterial liquid, and i also place a condistion block in the unit, but most of these methods only seem to help little. Things like water filtration, and soft water I'm sure would make much better improvements to staving off sediment, and scale build-up. Here, I'm generally replacing Pads-Panels once a year, and due to many nasty dust storms we get over here, I try to stay on top of Resovoir maintainence. Deifnitely do make sure your Pump sits in some sort of Basket, and if you can, pullit periodically to clean with an acidic product. Believe it or not, I use "The Works" Toilet Bowl Cleaner on the pump's bottom grids, and the Basket. When the basket looks really poor, dump it, and replace, they're only $2-$3 ea.
A Spider Snake can come in handy to clean out clogged water tubes, and do make sure proper float level is correct for your unit, not too much, or too little.
I'm typically up on my roof doing this 3-4 times a season to get optimum performance.
With whole house Swamp Coolers, I had found mine was seeming to give awefully poor air flow, just not enough ommph. What I did, was I replaced the stock pulley (12") with a smaller 10" Pulley on the Squirrel Cage. This helped by causing the squirrel cage to spin faster on either Low-or High Fan Speeds. (just like gears on a racing bike)
To then find the correct size Belt, all one has to do, is take a string to measure what the new belt needs to be for the new Pulley Combination. Tie the string in a knot, slip it off the pulleys, and then on your way to the local retailer.
Belts come in every size imaginable. of course there's a point one cannot go beyond woth Pulley swaps, as the motor may then be placed under more strain.
After any service is done, I always make sure that I leave one panel accessable, so I can see how everything is working before I button it all up, and come off the roof. One time I didn't do this, and the Hose going from the Water pump to Spider was pinched by one of the panels on my Square Cooler (Hose was a bit too long) I was wondering 'hey. it isn't that cool in here!?" Hope this helps you, Mark