My 2c worth:
1/ In my opinion it is all about trophies - and I do not see anything wrong with it. When you are old, you might have something else to look at than just your trusty TV. The wall full of trophies cannot be just dismissed as "you could buy it for $5 a piece". Win is a win, even if one is alone in a class. As one of my friends says about it: "History does not ask questions..." So, for the trophy, as well as for the good feeling and encouragement the winning provides, it might make sense to have more classes.
2/ I have a bit of issue with "production being cheaper that G2/G5/open class". Yes it is true--if you build a true G2/G5/open. However, the production class MUST be all production and G2 MIGHT, but does not but does not have to be a true G2.
Which means that I can build a sturdier car for the same money or cheaper--if I choose to race a car which is close to being "production" in G2/G5/open class. I can go to a junk yard and pick up a transmission from any VW to put it into my “G2” car for $300. In the production class I have to have the same transmission as it was originally in the car. It might be much more difficult to get, not as sturdy and possibly more expensive.
Obviously, one might have a huge problem to win with a "production" car in the open class, but for this argument see point (1) above. If one does not care about “fairly level playing field” (a difficult concept even if you have many classes), than it makes more sense to have just two classes.
Furthermore, the open class is scalable – as I have more money I can increase the power of the car almost without limits. With a production car, I am at the limit almost from the beginning and to get any incremental improvement costs me more than to do the same with the production car in the G2/G5/open class.
In the end, it is often the cost of going to events that overrides the car specification. For example, if I go to all CRC rallies (East and West), I would probably do quite well, even if I do not place great in any one of them.
I am for two classes only, but it might be coloured by my perception that even in the full spec open class car I might not have any trophies anyways (to paraphrase Jamie; “one word: NoSprongl”
).