Getting management to move from green screen

Has anyone succeeded in getting their management to move from their 
tried and true green screen PickBASIC application to a more modern 
interface/software structure? What economic benefits can you propose? 
After all, doing so would mean rewriting and/or subroutining (? Hello 
Websters Dictionary) the whole application. (Has anyone done it
piecemeal?)

Our green screen application might not be pretty, but it's terrific. 
 From the end-user's perspective it's quite efficient heads-down (even 
if a little cumbersome at times because you can't pop up windows at 
will). From managements perspective it's great - it runs the business 
well and it's cost-effective to run and develop. And we are constantly 
adding enhancements to it - to make life easier for the end-user, as 
well as to improve the business bottom line. And, yes, we have developed 
interfaces to Windows applications - Word, Excel, UPS Word****p, etc. So 
there really seems to me to be little economic justification for moving 
from green screen, PickBASIC to anything more modern.

Is that true? Are there significant benefits to a revamping? Does anyone 
have real life experience in this area? Are there really sufficient 
cost-savings to warrant the huge expenditure? Can VB.NET, DesignBais, 
whatever, really be cost-justified?

(I'm not talking about moving from MV. We'll stick with that. I'm merely 
talking about the software interfacing to the data. And I'm also not 
talking about a package being sold by a VAR, where saleability is a top 
priority. I'm talking about a home-grown package running a business.)

Sholom