Gibraltar remains a British overseas territory, with about 30,000 inhabitants. Gibraltar's economy is dominated by four main sectors – financial services, internet gaming, shipping and tourism, and while it is robust, its population is probably too small to host a significant stamp collecting community. Gibraltar's stamps are popular among British Commonwealth collectors, and the better items should do well based upon the growth of that market.
Though I often recommend obtaining expertization when buying stamps with overprints, in this case, expertization is not necessary, since there isn't a significant difference between the value of the basic stamps and that of the surcharged set.
Those interested in learning about investing in stamps should read the Guide to Philatelic Investing ($5), available on Kindle and easily accessible from any computer.