Codeshares never excite me. It's a barely-better-than-nothing action on the part of an airline, IMHO.

My reasons:

• Without any alliance membership (discussed above, and - no - it's unlikely to ever happen) there are no reciprocal FF customer benefits -- other than with DL. If you're a frequent traveller, those benefits are really important. If, as a WS Platinum member, I fly on any airline (other than Delta) ... I get nothing. I'm a totally unknown traveller to WestJet's codeshare partner, meaning back of the long check-in line, using the slow security line, boarding zone 19, etc if I'm travelling in Y. Fine for the once-every-year-or-two leisure traveller. But not for me.
• WS codeshares and interlines are finicky, to say the least. I have yet to have a good, seamless experience with WS plus a partner ... like the experience that is available from airlines who are part of an actual alliance. Flights within Star Alliance really do work (almost) like one big airline. Same for SkyTeam (at least DL/AM). But not so much when independent airlines slap their flight numbers on each others' flights.
• Regardless of the airline, I'm always reluctant to book a codeshare flight number -- for the reasons above. From many years of flying, my experience has taught me that things typically go much better if I buy a WS flight number for a WS flight, a DL flight number for a DL flight, an AM flight number on an AM flight, etc, etc.