Have used the 'higher' versions over the past 15 yrs. I currently have both QW06 Basic and Delx versions running on separate systems and have swapped the same fileset between the two with no problems and perhaps some interesting results.
Basic does not include the file attachment feature [new in QW06] - it seems to just ignore them. Basic does not include QW's version of the 401k acct. Interestingly, recent testing indicates Basic will display a 401k created in Delx - appears to be fully functional but have not thoroughly vetted this. The 401k account type is normally handled in Basic using a tax-deferred brokerage account - as in the days before QW added the specific acct type. Basic does not include the ESPP acct feature but appears to accept one created in Delx. Again have not thoroughly vetted this observation. Basic does not include the assortment of 'planners', extra investment analysis tools, budget alerts, etc. 'Higher' versions include some pre-configured tax forms [Sched D, etc] but I find QW's Cap Gains and Tax Schedule Reports provide all the info I need for tax reporting.
My observation is that the core financial management systems are virtually the same [with the above exceptions] - account types, downloading capabilities, reporting, etc. Currently track checking, savings, credit card, brokerage accounts and rental properties in Basic. If one finds the 'bells & whistles' useful, by all means go for it. I don't use them and find Basic does everthing I need.
I would use the Tax Planner if it was more versatile but find it far too conservative for my situation. I use the most recent version of TTax tax planning.