Perhaps your confusion may be as a result of how some people describe their maps. From what I've encountered (which is not alot by any means, but perhaps helpful nonetheless) is that there different levels of tune.
Stage 1 is a software upgrade which basically allows the stock components a bit more freedom.
Stage 2 involves upgrading the air flow both in to and out of the engine (air intake, exhaust and intercooler). At this stage some people have the software on the car tweaked in order to make the most of the recently upgraded components - this would be a stage 2 map.
However some maps can compensate if the air flow in the engine is increased (for example when upgrading from stage 1 to stage 2). These sorts of maps I have heard being called a Stage 1.5 map (and even a straight stage 2 map) however this is only a name and does not really mean that it is a completely separate map to a standard stage 1 map.
Obviously there are more stages after 2 but I'm not the most experienced so I'll keep my quiet.
As for upgrading the intercooler, yes ambient temperatures can have a part to play, and if you're car suffers a significant loss of power in summer then an intercooler would be a worthwhile investment (if turbocharged of course). But from a modification point of view, it simply keeps the air in the system cooler (and therefore more dense) thus allowing the car to pull strongly throughout the rev range. By way of example my recent MINI R56 JCW (which has a piddly small intercooler) struggled on a Rolling Road because the engine was reaching certain temperatures after 4.5k rpm and the ECU was protectively overriding and shutting down. With an upgraded intercooler, the engine won't reach those dangerous temperatures as quickly and so the ECU won't have to limit performance.
Hope all this helps.
