My experience is that larger wire gauge enhances signal strength on the track. When I built my layout in the early 90s, before DCS, I used 14-gauge throughout, except I had some 16 toggled blocks at the far end of the layout under the main layout, for layovers. To save effort, I used 18-gauge multi-conductor cable--what the heck, I'll have ny jand on the throttle anyway as trains go into those areas, so I can apply a little more power to overconme voltage drop.
When DCS came along, and I inserted the TIUs between transformer and control panel. The 14-gauge blocks had great signal strength; the 18-gauge blocks were pitiful. Eventually I rewired all 16 18-gauge blocks with 14 gauge wire, and signal strength was no longer a problem.
Incidentally, I do not use twisted pairs, on the theory that wires that close together have increased capacitance. All ground is via a 12-gauge buss loop that goes around the layout.
