I would add the only value to upgrading is to you and your enjoyment. When trying to resell ,most parts don't add any value to most buyers. They mostly will only pay the going price of a stock bike. It's also not a great idea to think that you will move parts over to a new bike, that doesn't happen much . The parts that you might move are saddle and peddles, almost anything else will be a upgrade from what you already have plus it will be new.