IMHO, the only way that Delta can improve biz-elite to make it more attractive to passengers who HAVEN'T already flown it is to make the seats fully flat. Having just done a round trip LGW-ATL in biz-elite on 767-300ERs, I reckon it's one of, if not the, most comfortable places to be for 9 hours!
When designing it, I'm guessing that Delta must have asked themselves did they really need a 'true' First Class for trans-atlantic flights (their biggest international market)? Jaysit is right in that not many firms will pay first class fares, so flying an enhanced business product (eg. DL Bizelite or CO Bizfirst) is the way to go!
Also - as best i can tell, DL is having no trouble filling biz-elite on most flights. So, if it ain't broke, why fix it?
The only thing I would change is to serve their fantastic cookies with every meal - not just lunch!