A big part of being a collector is which mentality you choose to follow. For me, and it was something I had to learn (so it can be done!), it has greatly helped to realize that you
can part with items and it's OK. It becomes easier the more you do it. You'll find another copy of X card if it's meant to be, or something even more appealing to the future version of yourself will inevitably appear. Appreciate what you have, but don't squeeze the cards too closely to your heart. They are pieces of cardboard that bring enjoyment, but let them visit you for a while on their journeys then allow them to move on if that's how it's to be.
If the card and price points check out and it's something that you can afford without strain, just buy it. If you do find yourself pressed to sell down the road and end up making a tidy profit, you just might find your whole mentality changed on your behalf due to that nice flip you made!