I agree about Spruce. The Rams need a reliable, move-the-chains, Ricky Proehl-type WR in this offense and it could be him (next year).
With Higbee, at least he is getting targeted more now with Goff starting (8 in the past 3 games, 4 catches). I saw multiple times being at the Saints and Patriots games him run downfield routes and Goff looked at him as his primary but then went to his next read. He has 7 catches right now and may end up with 13-15 by the end of the season which isn't bad for a rookie backup TE.
Whoever the coach is in 2017 their focus in the passing game (beyond upgrading the OL of course) is getting Goff, Cooper, Higbee and Spruce all much more comfortable and ready to contribute.