The short answer is yes, you can wear a diamond necklace everyday with just about any outfit. However, certain diamond necklace styles are more appropriate for everyday wear than others. For example, a diamond pendant necklace or diamond solitaire necklace are usually more suited for everyday wear than a diamond tennis necklace - both in terms of fashion pairings, design, durability, and price (diamond tennis necklaces are quite expensive and generally more formal, so most wearers probably wouldn't go to the grocery store in a diamond tennis necklace).

Diamond necklaces have always been and likely will always considered to be trendy or in fashion. Trends may come and go, but diamond necklaces are a timeless staple in the world of jewelry due to their versatility and brilliance.

Diamond necklaces will generally hold their value over time, but that depends greatly on market fluctuations and the quality of the materials and craftsmanship used. Diamonds and gold, specifically, show no signs of losing their value amongst modern and future society, so gemstone and precious metal necklaces should continue to maintain a high resale value.