This is such a nice piece!
The guitar adds such a cool warm tone to it and the strings/woods and high piano do a good job of setting a peaceful/romantic mood.
Have you tried adding a triplet feel shaker to one of the sections? It's just what I'm hearing would go in my head and I think it would add a nice contrast between two different sections.
I love the other subtle pieces of percussion you've used too though.
Great piece! :)