I think there's gains to be had. Out of intetest when I had my clio turbo'd I had the open port on the underside on my inlet plugged then ally welded.
Car made 341bhp @1 bar of boost at RStuning. No one else could replicate it for the same boost and a few people hinted that Paul had maybe fudged the dyno results.
Apart from Blighty, he managed 340bhp on Scoffs dyno using the same set up I had, he was also the person who bought my plugged inlet from me. I think the flow from the stock inlet is good but I also think there's some boost leak from the underside seal.