Set the key weight to maximum if you already haven't to achieve better dynamic control and to be able to play pianissimo possibile, with lower settings best you can do is a mezzo piano, but realize that it is going to make things much more difficult, and playing the agitato part will be particularly nasty.
Voicing is the first obstacle that stands in your way to master this piece. Put more power to the two high notes when you play the three note motif. You should be voicing the top notes of each chord, but I don't know if voicing the top note of the left hand chords is a good idea, find out the voicing yourself but never play all the notes evenly. Do this until the grand finale begins. Also, never play broken chords. It's a bell motive. Pedalling is not difficult, for obvious reasons, but if you have a sostenuto pedal, which I think you do, you can make things interesting.
I can imagine the unusual fingering of the chords confusing you at first sight. But you don't have to follow them if you think it's easier to play it the other way. Also, a tip, you can play the top notes with your 4th finger to have better control over the voicing. If you play with interlocked hands, you will most likely voice the top AND the bottom notes of each chord, because you will be stretching your hands for the octaves. Unless, you have hands nearly as big as Rachmaninoff's. If you don't play with interlocked hands, and try to use the 4th finger, you will be instinctually playing broken chords to not voice the middle note. So you will have to actually think while playing. But this way, pressing the keys at the same time will most definitely be much easier than playing with hands crossed. Also, it is correct that playing the chords forte makes it easier to play the notes at the same time. I also have to warn you, you can't trust your muscle memory if you're going to take an alternate route. Doesn't matter if pedalling or fingering. You may rely on the pedal, since sliding is difficult, even for the majority of the forum members.
I press the pedal half way down throughout the entire agitato section. Starting slow, then speeding up gradually (or doing anything to create tension), and using effective rubato (but not overusing it) on places where you see fit will definetely improve your musicality. I see you lack control over dynamics and tempo particulary in the agitato section. Work on that, but never play inégal, for the sake of our ears.
Altough I don't think Rachmaninoff composed any program music for piano, except some obvious ones, this piece has a story, I heard. You may read it, which I don't recommend until you polish the interpretation into your final, since Rachmaninoff himself has opposed this, even with his Etudes-Tableaux, but later had to tell Respighi, who orchestrated some of them. You can make up a story of your own, or just define which emotions the passages represent, on a larger scale. This will help too.
Good luck with the piece! (BTW, I liked your interpretation of the Chopin waltz, which needs some more work. But if you were to polish that, you would do wonders with it.