depends on the DLP with a lower end unit you could well see an increase. Hi end (Barco Cine 80 etc doubt it) also depends on the scaler a really top scaler will probably do wonders for a mid range DLP. a cheap one may add a little.
Pixelworks are a manufacturer of scaling chipsets. Some of their products are used in things like the SIM2 range and, I believe, the TAG scaler. Having said that there is more to a scaler than the scaling engine. First you need to get the analogue information digitised and sent to the de-interlacing solution. Then once it's scaled it often needs to be turned in to analogue again before coming out of the product. All these stages are important to the end result,
As has been mentioned you need to evaluate each case on it's own merit by doing a demo.