Grandpa always told me "you'll never go broke taking a profit when it's in front of you"...
I am kind of in the same situation, and asking myself the same question. I calved out a set of heifers last spring - weaned the calves, backgrounded them for ~60 days or so and sold them. I paid $1060 for the heifers as open replacements, and got right around that for the calves. So here I sit with paid for 3 yr old second calvers - that are worth ~$2000 - $2500 a piece around here. Like KT, I am not going to pay that for a bred heifer - it's going to take her too long to pay for herself.
In my simple mind, the math works like this...we might see $1000+ calves for the next couple years. I doubt it goes too much higher, certainly could go lower (some type of black swan event in world economics, etc.). So you get $1000/yr for the calves, it takes you AT LEAST $1/day to carry that cow all year (certainly could be more). So you'll net somewhere around $650-700/year on that cow, possibly less.
It's going to take the new owner three years to re-coup the initial investment on the $2000-2500 heifer. I am not willing to hold on to that heifer/cow to generate the same dollar amount over the next three years. I really think that there is nothing wrong with taking the money, and doubling down on something at half the price (older cows, open replacement heifers, etc.). It's all about risk tolerance and where you think the market is headed.
In your scenario, where you are at right now, and what I have done. I would breed them back, sell the calves after weaning (hopefully you'll get your initial $1050 back when they calves are ~ 7 months old) and then see where the bred market is - it's usually higher for 2nd calvers, if it is where you need it to be - sell the cows; you will have grossed 3x the initial investment in ~2 years. If the bred market is not where you need it, you are still "own the factory". The risk in this scenario is the cows not breeding back, or the market tanking in the mean time.
What do I know, I am just a rambling multiplier...