Congratz!! Glad you finally got that heavy you have been wanting for so long, I guess she gets top priority on the lvling list?
SC spending can be quite cruel, where it is true I have had a handful of good runs with it, there is a lot of bad runs too, though I have a lot of gold spares for lvling should I need but I am holding onto them for this gold unit trading in system I have heard about.
I am currently focusing my efforts on lvling my team before I buy any more units, want to have most lvled before we get bombed with new events and content (Should that ever be the case).
As for the valks, it depends what you want to get out of them. Like you I don't need the valks to be a duelist as I have others who are much more powerful in that department so I use valks as a sub duelist should I need them or for there ability to give UP and good recall value. I have Elanie, Kerry, Emilia, Thetis and Dahlia.
But I really only use Elanie as my main valk and reason being is she is my cheapest valk so I can deploy her quickly and she can hold her own, even as a lightning rod. I have lvled up Kerry and Emilia as back ups should I need someone more powerful but if you only need them to valk stuff then Elanie works just fine.
If you are looking for one of the two higher ones to take her place though I would say choose Kerry, Emilia isn't a bad unit with her skill but Kerrys base stats top Emilias and Emilia will really only come into her own once her skill is active but you would only really need that if she was going to be a duelist and that would only work in some situations that Kerry couldn't already handle. I believe your time would be better spent on Kerry, she is a better base valk that Emilia so you can throw her into most situations no issue where Emilia would still be good but not at Kerry's lvl unless her skill is active.
As a valk Elanie is your best option as she is cheap to deploy and also has better base stats at max CC than Emilia (Except health my a small margin), the only reason you would choose Kerry over her is if you wanted someone more powerful. Also you only lose a couple UP with Elanie and Kerry with no CR compared to Emilias max CR, I don't believe you will find many situations where 1-3 UP will matter when you are using a valk to gain UP.
In the end though I guess it is what you feel is better, I believe your time would be better spent on Kerry.