Welcome to the Q&A Forum

I don't think the URLs are an absolute disaster. Before making any changes like this you need to understand the potential risks and clearly define what it is you are trying to achieve. Look at how many links/linking domains each of your pages have. It's these deep links that are both the most valuable to the pages and also the ones most at risk. How many pages do you have on your site, how much organic search traffic do you already attract? Where are you currently ranking for your chosen keywords? If you've got lots of deep inbound links and the URLs aren't causing a significant problem then I don't think I'd take the risk. Even if it all goes well, you'll lost some "link juice" in the redirects. What will be the return on investment of your time re-structuring your URLs and 301 redirecting all the content to the new pages vs the potential loss of rankings/traffic? Hope this helps.