I would keep a few, 2-3, and sell the rest to pay the mortgage. I'm actually going to be paying my mortgage off this month. Unfortunately, it's not the way I would have wanted to as it's from the loss of my mother. I know there's a lot of people, and being someone interested in the stock market and investments I get it, who say the money could earn 6-7% relatively conservatively, why would you sink that much into something that's just 4% interest? The home mortgage is a great bet, even Warren Buffet says so!
But, at the end of the day, it's peace of mind. The economy can tank, jobs can be lost, unexpected major expenses like HVAC replacement or roofs can happen at any time. Knowing you've safe guarded yourself against a lot of this and are in a position to live life more carefree is more valuable than the extra growth you *may* get to enjoy down the road. Back to mother, she died suddenly of, we think, sudden cardiac arrest at 62 two days before this past Christmas. Was a complete shock and one thing it's made me learn the hard way is how we really don't know the time we have. Having the ability to enjoy life a bit more in the moment than earn "x" amount more over 20 years could be massive if you won't be around in those 20 years.
The amount of money you'll save monthly too opens you up to re-buy your pinball collection too, fairly quickly if you're saving $2400 a month from losing it. Once you have the games back you want after 2-3 years, then you've got an extra $30k a year in your pocket that you can do whatever you want with -- travel, invest, a new car, etc. Lots of interest saved too along the way. I don't think you will regret it and, I know it's a constant debate on here, but I think pins are at a pretty high point now. You may get lucky and sell, pay this mortgage and, potentially, buy back in a worse economy or worse pinball market.