Willie, perfectly convincing stereo-field placement of Dimension instruments certainly can be done in Logic. It's a matter of exploiting the 1-close-dry-mic-per-instrument advantage of Dimension, and using Logic's built-in mono-to-stereo Binaural Panners on each dry single-instrument mono audio feed from the library player. (Libraries of sampled ensembles require different spatialisation treatments, but we're talking about the wonderfully flexible Dimension libraries here.) One complicating factor for this dry mono source approach is that the VI players have limited audio routing compared to the Synchronised version - but with some effort and ingenuity it can still be done.
Stereo room or hall acoustic ambiences can be readily and very flexibly simulated by applying reverb plugins to the binaurally panned instruments, either singly or in any sort of groupings you find work best for realism and/or the artistic effect you want. In this case I find using a Balance control on each reverb's stereo output can - with some crafty touches here and there - put the instruments convincingly in an acoustically live room or hall. For example, you can very simply make one stereo reverb plugin instance emphasise (without overdoing it) left reflections for 1st violins, while another reverb instance emphasises right reflections for Cellos. Also, each reverb instance can be set up for slightly different reverb character, including use of wet/dry/predelay also, in order to simulate asymmetries in the various reflection paths, left/right and near/far.
You'll find that once you've applied binaural panning well to place your dry instruments in their various groupings, the ear really doesn't need any more convincing as to what's where in the stereo field. Reverb is then only about the shape, size and reflective character of the reverberant environment surrounding the players and audience.
Logic's own reverbs will get you going and ChromaVerb especially is a good way to start getting the hang of what can be achieved with today's algorithmic reverbs. Bear in mind scoring stages for film work typically have tails of around 1.6 to 2 seconds, whereas the tails in some large concert venues may stretch out longer. Adjusting decay time is the easy bit, compared to developing your understanding and skills in how damping profiles and pre- and post-eq profiles work together to give character to a simulated reverberant environment.
I think you'll find you'll soon be getting great results with what you already have at hand in Logic. Unless you're already a busy pro composer who has little or no off-project time to spare, I'd say it's a case of building your own knowledge, skills and experience in using the various spatialisation effects (and there's no end to it!), while of course often comparing your results as critically as you possibly can with the best examples of recorded film scores, concerts, and what have you. The Dimension libraries offer a truly excellent grounding - and they'll let you get flying sooner rather than later!