Most likely, you do not need to replace that wheel but have it properly rebuilt and tensioned. I'm surprised the lbs has not suggested this after the second trip. Perhaps they do not have a qualified wheelsmith and do only minor repairs but that would be surprising. If you buy a new wheel, you really should go through the same effort. Get it properly tensioned. This is the most important factor in longevity. I suspect that your original wheel was never done right - few are. Each time you replace a spoke, you are just getting the weakest one. If your wheel is not properly tensioned right now, you are dramatically shortening the life of even the new spokes that you have replaced. I would recommend that you have both wheels looked at by a qualified wheelsmith. This is money wisely spent and will reward you with many miles of use.