As you can see, its pretty apparent that this is an area specific question. As a Santa Rosa resident, I do not have central air and do just fine. Here it is NOT a given by any means. Temperature control can be easily achieved if you take advantage of our natural air conditioning....coastal fog and nightly cool down. Windows open late afternoon/evening......closed in the morning. The house, if well insulated, stays pleasant all day. There are perhaps 5-7 days each year where I wish I had AC....and I get over that quickly. Sonoma gets quite a bit warmer than Santa Rosa, making it a bit more of an issue,but still not a given. As far as it affecting the sale, when doing a market analysis, I usually discount a basic home $5000 for no AC....a larger home requiring a more expensive system would, of course, require more of a discount. As with any amenity, some buyers would put central air on their "must have" list, in which case a credit or price reduction could be negotiated, others could care less.
Best of luck to you