Data data and more data...when is too much a concern...when / if should a business go to a content management system.

I have several clients in their daily business that use normal standards accumulating data, regular MS Office documents (word, power-point, excel, etc), pdf's, images (jpegs, mpegs) moved into a folder structure on a server from one form or another, sometimes USB drives, from email, etc.  As you can imagine 200G turns into 400G, 600G, where we expand out the drive space we're now facing close to 2T of data and rather than expand the drives to 4T I'd like to the experts recommendations moving forward with this current situation, how to limit data growth in a situation like this. In my defense this was never neglect more so three clients were small and increased 10 folds literally within six months from hiring new staff to the amount of data coming in. I'm interested not only how to proceed with data management but old habits die hard, it's like pulling teeth walking into my clients office and mentioning a content management system or archiving, grown men and woman letting out "sighs"..."but we like the way our system is setup"...and they chuckle. I do enjoy seeing my clients happy but I have to draw the line when backups, data integrity, future planning / growth come into mind and I prepare the best way to move forward as they continue to grow. While everything is fine now I would like to take on this project and either archive old data or move to a content management system, what are everyone’s thoughts regarding this? How to pull archived data up if needed, where to archive (local server, NAS, offsite, on a USB). If going with a content management system which one, Imanage is expensive and cumbersome in my opinion, Worldox not bad but not sure the more users the system seems limited, and then there’s SharePoint. With a content management system how do you get them to understand how it works and feel good about it before going with a full solution (do not like the feeling of moving close to 2T of data into a content management system, whatever system it is, and then finding out it’s not what my client cares to do daily business with). I understand could take a small chunk of data to test but that's where you all come in, I've spent days testing numerous products and support in the trial phase where support bends over backwards to make sure you're happy only after a purchase you can't find them if needed, then I’m left with the ball. I understand all the products well enough because I’ve been around them long enough and provided support but with each version is a new flavor etc. We all know the fun involved evaluating new products, bringing them to life while continuing to keep or clients happy can get tricky.

I look forward hearing from EE your feedback is invaluable.