Malta has gone through a few iterations of falling in and out of favor with collectors over the past few decades. However, some of the core topicals will always do well, especially post-1980's topicals. In particular, space, mushrooms, ships, to name a few, have done (or continue to do) especially well recently. So you will find the catalog prices for topical stamps from relatively obscure countries with a respectable premium -- Bhutan, Tanzania, Guinea-Bissau (many topical sets now catalog $10+)...
Then there are some novelty topicals, such as sports paraphernalia, space aliens, which have catalog values of $10+/$100+. I wish I could find my power cord for my scanner, I would post a few pics. I've purchased them over the years not for topical collecting, but I thought they were "interesting" collecting specialties and wanted and example to remember "collecting history". If I ever find my power cord or get a replacement, I'll try to upload some pics.

k