Regarding Past + Present, there is a new edition being worked on by Roger Gillham. However, no publication date has been set and it is not due for some time, so don't let this put you off from buying it.
It is an excellent book and I'd recommend it to anyone interested in Scalextric.
Regarding Super 124, it was quite a limited range and only lasted 3 years. Only 6 different cars were made and a similar number of track sections. The track still sells for good money, and some of the cars go for up to £1,000 (or more).
Jon,
Slot City.