I'm not sure if users will pay for XLC calcs per say but then again companies often employ others for design services so there may be something in it if it is packaged correctly.

You could use its contacts here to offer engineering design services over the internet. But first you need a list of consultants, CVs, testimonials etc and then need to sell this service to companies (perhaps under the Morevision or some other umbrella, operating as an agency but essentially growing your company into an online engineering consultancy with worldwide contacts and resources).

Rather than making this an after thought to excelcalcs.com, I would suggest that you sell this service through a dedicated site (although, as above, this site may prove a useful way to build a list of engineering consultants).