I thought about this some more and decided to hunt around and see what I can find about using base malts to help extract brews. Here's an article where they talk about using base malt to help with aroma of extract brews:
http://beerandwinejournal.com/add-base-malts-to-your-extract-beers/
Chris Colby covered the subject for BYO magazine, again the aroma component is discussed:
https://byo.com/malt/item/2543-converting-to-partial-mash
And Brulosophy did a comparison between All LME Maris Otter and
All Grain Maris Otter (Crisp Floor Malted):
http://brulosophy.com/2014/07/21/extract-vs-all-grain-exbeeriment-results/
I was somewhat surprised that more than half of the tasting panel (57%) preferred the extract (All LME) brew. I was also surprised that the all LME beer finished at 1.011, my LME experiments, where I DIDN"T use 100% base malt extract, wouldn't ferment that low.
Also mentioned is that a 5 gallon batch with all Maris Otter extract cost $28 versus $11 for the all grain (purchased in bulk).
So if you make your kits with more grain and less extract, you can bring the price down.
He also talks about a survey he did that gives some interesting information about how homebrewers got started. 59% said they used extract and steeping grains, 22% said all extract.
Although I have never used an ingredient kit, it appears that many others HAVE used them so The OP's experiments in making better extract kits could pay off.
My limited experience with extracts has made me not want to use them except in certain circumstances, and I'm thinking the only all extract beer I would like would be a hop forward beer, or maybe something with a fruit or yeast character. But I still think extract is worth experimenting with.