The topic is so broad that any perspective counts, so I take my chance to present my own analysis referring to three basic categories, the vintage, the heritage, the homage models.
Vintage models are old timepieces, theoretically at least 25 years old, with most of them bearing significant collectability. The best ones maintain market prices higher than the respective contemporary line models. One interesting sub-category is New Old Projects (NOP watches) created from the marriage of old and new materials, usually the fitting of old orphaned mechanisms into new wrist cases.
Heritage models are the ones re-issued (re-editions) from the original brands, usually after being discontinued for some years. This trend holds true for many historical models across the industry, with all brands maintaining their original designs, and applying necessary improvements.
Homage models are qualitative substitutes of the vintage and heritage ones since they are affordable, produced usually by micro-brands, with emulated designs inspired by specific collectible vintage models, like pilot/military watch instruments, or diver models presented in 1950s/60s. Four interesting sub-categories are the generic TACHYMETER/TELEMETER chronographs, the MARINE style models inspired by deckwatches, the EXBO and EXPO watches. EXBO (ex-board) models referring primarily to wristwatches with dials inspired by the clock instruments installed in aircraft cockpits throughout the aviation history, plus dials inspired by clocks installed in historical car model dashboards. EXPO (ex-pocket) models referring to wrist watches equipped with dials inspired from classic pocket watches of the 19th and 20th century, and preferably equipped with contemporary large mechanisms (of pocket origin) like the highly respected ETA/UNITAS 6497/98 caliber.