I'd buy the new XITE-1 when its released if you could afford it, but the SCOPE cards you mentioned are still great aswell they just won't offer all the power and benifits as XITE-1 and is less future proof. The ideal thing to do i suppose is to buy a small card and check out the plugins and if you like them then buy XITE.
The 15 dsp booster you mentioned may be upgradable, i'd look into it cause many great plugins come with SCOPE Professional.The SCOPE Professional has both 'Synths&samplers pack (unrivalled)' and "mix& Mastering pack", both packs have alot of great plugins included and both packs are included with the 4.5 version of SCOPE Professional. One of the packs is included in SCOPE Project card 4.5 also. If both those cards is not 4.5 platform then you'll need to pay a small upgrade fee for the one/s that can be upgraded, it is a very small fee considering all the quality plugins you'll get. The other stock effects on both cards are generally pretty good but also a mixed basket imo, i do prefer SCOPE Stock over any other stock plugs from any other programs i've tried tho, but most of the really juicy ones are with Third-party developers wich you'd want to get a list of. Some pretty good freeware also (very pro sounding). Basically see if you can upgrade the booster if not then the Project card if it is'nt 4.5.
In the past i used SCOPE with uad-1 and had no problems. If you buy the cards and don't like them they still should have a good resale value but it's hard to not like the most powerfullest Platform out here

.. I'd really consider XITE-1 if you can afford it if not the smaller cards are still great and will be for a long time still.