There was an earlier thread on this topic that you should probably try to find but in a brief summary, Cruising spinackers do help a when sailing at high wind angles. They are not really down wind sails in the same way that a symetrical chute is a downwind sail. They are at their best at true wind angles between 90 and 150 or so degrees. A conventional symetrical chute would be more effective (and easier to fly)on a boat like the Coronado 25.
A couple pointers on going dead downwind. Most people do not ease their mainsails enough. Going dead down wind is about projected sail area not shape. The boom should nearly touch the shrouds and you should have reasonably high vang tension. In a slightly contradictory point ease the outhaul and mainhalyard slightly. Get yourself a good whiskerpole and pole your gneoa. If you have a knotmeter, in lighter winds, see of pointing up maybe 15-20 degrees does not yield a significantly faster speed through the water (Typically a knot or more on a more modern design). If so it may really make sense to "tack down wind" in lighter winds.