I've never used PS Elements so I can't comment on what is lacks as compared to Photoshop CS2. Premiere Elements is for editing of videos tailored to home users so it has no apparent use in conjunction with Flexi or with
sign making.
I am also an Omega and Flexi user and my decision was to license the entire Creative Suite Professional package. The combined suite allows me to deal with any file anyone provides for production and fills in the many gaps and shortcomings of Omega and Flexisign.
Creative Suite is a lot more money for sure and I figure it took me the better part of a week to get a complete ROI with it. I am of course being sarcastic but also truthful. The Creative Suite is largely the standard of the professional community. I cannot imagine trying to operate without at least the full current versions of both Photoshop and Illustrator and I also use Acrobat Pro regularly. The standard for universal file exchange is changing from EPS to PDF and Illustrator is the essential tool to get PDF's opened and brought into your production software such as Omega or Flexi with consistent accuracy.