Paul - even if you were to buy the software - or say upgrade on the old model from CS5.5 to CC15 - the upgrades were roughly €600 - not sure what that is in Pounds... anyway - the cloud subscription is only 24.99 per month for the software (where you can purchase 1 month only if you wish).
Even still over 1 year that's €299 per year.
CS5.5 was in 2010 - even better CS6 was released in 2011.
So in the 4 years since CS6 you would have to upgrade 4 times at the tune of €600 a year - that's a whopping €2400.
With the CC subscription, 4 years only costs €1200.
What I'm saying - even if you stayed on CS5.5 and continued working on files that were sent to you in cS6 to Cs15 - then you'd still need to request files in the older format of IDML.
That being said - if you do get newer files - you can purchase a single app use for 1 month, and do the conversion yourself, for €24.99.
@Levi
I understand that you want 'Ownership' of the software. Lets be reminded that software is only ever Licensed to the End User - it's always been leased, that's the same with fonts and any type of software. You have paid for the license to use the application, but the ownership remains with the author who holds the rights of copyright of software, distribution, sale and copy etc.
Cloud features are additional to use if you want - you don't have to use the Cloud Services. You will always retain the ownership to your work - Adobe cannot and will never see your Files. The only thing that happens that's a bit shit is that if your Subscription Lapses you can't access the software to open the source files.
I love the Creative Cloud and it gives me full access to the entire Adobe Suite to do any project that comes up, from Sound to Video editing, presentations, books, epubs, animations, web, etc.
All Apps - all in - €64.99 a month.
If I'm not making €64.99 a month then I"m in the wrong business!
Plus I can push the costs of the subscription to the client.
The best thing about being part of the cloud - your apps are always up to date.