I also believe that increasing P.R. and advertising is useful even if all cars are sold out.
1st, it increases brand awareness as has been pointed out by others. This is important because the Elise buzz won't last forever.
2nd, you want to do this when you have a hot and favorably regarded product. That way the positive impression you are trying to create is backed up by the actual product itself, and the favorable opinions and reviews garnered by same.
3rd, they need to expand their core audience for the day when all the dedicated Lotus fanatics have bought their cars. This type of talk always ticks off purists, but to avoid having the tenuous existence which has been Lotus' history the past 40 years, they need to have a bit larger audience than they traditionally had.
4th, Lotus needs to establish their name because in the future, they may see competition in their niche (how many other manufacturers are preparing small, light sports cars?) If they establish themselves as the premier name in this niche, it will help them survive heavy competition by having a premium name and reputation.
I give the iPod as an example. This has been established as the benchmark that portable music players aspire to, and Apple is regarded as the hip, premier maker of these devices. Now, even though other companies are trying to knock them off, and a few actually have favorable reviews compared to the iPod, the iPod still rules in terms of people's thinking and purchasing. It's an uphill battle for other makers. If Lotus can establish this image, it will really pay off when other makers start competing in this market.
DLY