In the secondary market, Roman dial seem to be more demanding and better in price. If you check the auction prices for 5050, it is quite reasonable and really can be a daily watch! Perfect size! Don’t forget it comes with 2nd case back when you are looking for the watch in the market.
Congratulation Gordon! To complete one set like 5131 is amazing and it is definitely decent gift to your children. Therefore you should not split the set and start your new challenge journey for another set like Rousseau -The Dream or something different like new chronograph model like 5172 or old m
Buy what you like is important. I have both watch, 5131 is more attractive if you like hand craft watch. 5575 is only anniversary version and nice dial but you cannot compare it 5131 in term of craftsmanship. Of course you will not get wrong to take any one of them.