I run across this all the time too. Some landscaper just threw in some vista lights without any thought towards a good design or using solid connections and wiring practices. I give the customer the option both ways. 1. a price on a new system using the existing transformer with new wiring and fixtures, or 2. simply rewiring his existing lights and possibly repositioning some of them to make it look better. I'll reuse the transformer and fixtures, but I completely re-wire and usually put new sockets in the fixtures with a fresh lamp and a full cleaning. I charge time and material for this at my standard hourly labor rate. With solid wiring in the ground, they can simply upgrade their fixtures when the budget allows.
Vista's alluminum fixtures may not be the highest quality, but we all know it's the quality lamp and not the fixture that does the lighting. So, there is no reason to walk away from work staring you in the face going into winter. besides, when you are done it will look 100% better and they will be thrilled.