I can’t quite go along with your view that spread betting is not gambling. When you take a punt on whether a share will rise or fall then that is my definition of gambling.
I on the other hand, buy a share in a company because I want to own part of the business. I also want to share in its long-term improvements. So, whether the share rises or falls in the short term is somewhat irrelevant to me provided I believe in its long-term prospects. That is my definition of investing.
Robbie did say that the spreads on some AIM companies can be quite narrow. The spread will, however, depend greatly on the liquidity - the more liquid the share, the narrower the spread.