bamburg:
Since you are just considering it, I'd suggest you look into it quite a bit more before investing. In Germany, the militaria market is flooded with DDR militaria - so much so that the market has (IMHO) collapsed. DDR militaria is often given away at the German flea markets just to get rid of it. If you're dead set on it, then look at it as a good time to jump in and build your collection with minimum investment for the next few decades as the market rebuilds. Since it's so plentiful, it's usually cheaper to buy originals rather than making copies. There's a lot of hype about DDR items but reality doesn't support it. Complete DDR uniforms often go for about €20 at flea markets and then they're often to be used as a Karnival costume or converting to a 3rd Reich uniform or something. Since you've been collecting for 20 years, I find it somewhat amazing that you'd seriously consider this field. If you like, I can expound on this a bit but it's just a "quick and dirty" summary.
Imperial German (or German states) militaria would be a better investment for the same outlay because it offers a fairly quick turn-around profit but your knowledge base would have to be quite high. An 1870 Iron Cross 2nd Class can still be purchased for less than €200 (with bargaining) at flea markets which is far more expensive at a German dealer's. In the Imperial German militaria field, my best advice is to consider the subfield of colonial militaria - excellent potential but you need to be an expert before investing. Consider this: 1 specific Imperial German colonial medal with clasp(s) can currently be purchased for €100-€500 and the "book" value is often higher. You just have to look around. The current price increase runs about 10-35% per year depending on the item. Some of the items have varieties which have their own price structure and many non-specialist dealers don't know about identifying the variants (this is where the real profit kicks in for resell). Imperial German colonial uniforms can still be purchased and are currently not rare but this is expected to change within the next 10-20 years when they become rare. There's quite a few books/magazines available in Germany on this topic but usually have to be special ordered and most have not been translated into English.
I'll reserve comments about WWI German militaria until specifically requested. Another good field but you need to know what you're doing.
Personally, I never recommend consideration of 3rd Reich militaria - too many opportunities to be burned by fakes and too many collectors running around with limited knowledge.
