Thom, what would you suggest for effects that would unflatten (is that a word?) and thicken up the composition?
Aside from the obvious tracks that sound perfectly fine(the guitar & synths)...I would say that in terms of what could benefit from more effects,would be the brass and woodwind sounds.
I was thinking that a plate reverb,in combination with another effect to broaden the stereo field...would be good...because as is,they sound as though they were monaural.
Being that I don't know what your effects arsenal is like,it's very tricky to suggest what certain effects to add,because effects in general...vary greatly from one brand to another,in terms of their sonic character with regard to clarity,spatial depth & so on.
For example,some of my Reason reverb effects have wonderful preset combinations of plate reverbs & cross delays...whereas the chorus effects tend to dull the clarity of the sound.
In my Presonus S1 DAW,the chorus effects are amazing,in that they really widen the stereo field,without dulling the sound.
As for the bass track...well...ever since I really became serious about sweetening my bass presets with my newly acquired arsenal of bass amps & effects,I have become fanatical about authenticating my bass instruments as much as possible...by experimenting with many different amp and effect presets.
More specifically...really bringing the bass sounds more forward into the mix,by accentuating all of the little nuances of a real bass instrument...such as the glissandos,string buzzes & such.
I never used to pay very much attention to my bass sounds in the past,in terms of making them as realistic as possible...but Rony really jump-started my obsession into taking my bass lines more seriously.
In fact,I'm so much in love with electrified,acoustic bass sounds...that I rarely ever used synth basses.
As for the string tracks,they sound pretty good as is and I've realized that no amount of effects are going to compensate for a meticulously sampled string VST and the only really decent strings sounds that I have in my arsenal,is what's in my NI Komplete 6...but I am trying to get away from Native Instruments altogether,because I've had too many problems with installations and with virtually no customer support,I just can't bring myself to consider NI anymore(despite that I think that Kontakt is one of the best sample engines in the business).
If you're seriously considering making the adjustments I suggested,I hope my input is of some help to you.
-Thom