To put it simply, a 1080p projector makes a big difference and it's what our club went with (on my recommendation, as it happens).
1024x768 means 786,432 pixels - or about .79MP
However, if you have a dSLR with a 3:2 aspect ratio, you'll actually get 682 as your vertical resolution if you don't crop which means just 698,368 pixels displayed or about .7MP. If you go in portrait mode you get 512x786 = 393,216 or just under 0.4MP.
If you have a 1920x1080 projector (apart from the improved colour control, contrast ratio, DVI/HDMI connection etc which are all great things) you have a potential 2,073,600 pixles or just over 2MP - more than double your 1024x768. With a 3:2 images you can get 1620x1080 which is 1,749,600 pixels or nearly 1.75MP which is 2.5 times better than the 1024x768 in the same mode. For portrait you get 720x1080 = 777,600 which is nearly twice portrait on a 1024x768.
If you use a 720p projector you're really no better (and for portrait you're worse off) than a 1024x768 machine.
Yes they are more expensive, but the difference is very significant. You can have very large displays (get a quality screen, too) even in daylight (evening viewing with lights down, as you would likely have done with slides, is excellent). For those who shoot 4:3 there's still improvement and many photographers may even crop to 16:9 or stitch panos to that aspect etc to take advantage of the extra width. 16:9 is the future for these display mediums for the forseeable future, so it makes sense to get onboard.
If your club can afford it, it's very worthwhile. I would recommend LCD over DLP for this usage, too (nothing worse than DLP ripping that some people notice or the lack of colour saturation that tends to stand out with single DLP (3 DLP would be fine, but that's cinema level equipment far out of the budget of camera clubs), so 3 LCD is the answer.
Also, look for sponsorship from a local distributor or even from a manufacturer or consider teaming up with another local club who have different nights to you or something like that to help with the cost.
We spoke directly to the manufacturer for ours and got a unit at a very very good price because they saw the advantage in having their unit being used in a public manner like this.