Collecting antiques as a gerund phrase, acting as the subject of the sentence, emphasizes the act of collecting antiques, adding professionalism and depth to the sentence.
Present participle as an adjective: "pieces that might increase in value over time" with "increasing in value" as a present participle phrase, used as an adjective to describe the potential value of these antiques, adding detail and predictability to the sentence.
Past participle as an adjective: "vintage watches" with "vintage" as a past participle, used as an adjective to describe the age of the watches, adding descriptiveness and attractiveness to the sentence.
Conditional adverbial clause: "that might be undervalued now but could fetch a pretty penny later on" as a conditional adverbial clause, provides a prediction of possible financial gains in the future, enhancing the investment perspective and logical flow of the sentence.