Cataloguing my library

Is it another waste of time?  I've taken the plunge with LibraryThing. I'm not sure why.

I already have a database/inventory of my books in Access, including facility to track books I loan out. 
My real desire is to create MARC records - I've loved the first cataloguing subject in my course. 
No, well yes, but no, really what I need is to organise my books. 

My collection (of books [and games, kits, toys] is begging to be sorted ... I wonder how, after thirty years of devoted (okay: obsessive), orderly arrangement of my books, I can have shelved them so haphazardly and left them so for almost two years.  I remember when starting to shelve that it felt ridiculous to be taking the time (an excess of time because I am conflicted between Dewey and my own categories) to properly order the books when I had allowed my marriage to fall apart and was so fearful about how I would manage our life.  Waiting until I learn more about cataloguing in the library course (although I cannot conceive how it will ease the conflict) seemed like a reasonable justification, although the state of the shelves is a constant irritation.  For some time when I thought about tackling the task, it triggered the same guilt/fear complex so I guess I shall be grateful that such feelings have faded with time.  The last remaining obstacle is settling to a system of organisation - regretfully likely to be Dewey?

While I won't be creating the MARC myself, LibraryThing may help with the latter by telling me the Dewey classifications of my books, at least for those that have ISBNs.