I sailed on the WIllamette for 6 years and at Vancouver Lake for the last 5, and currently live in Vancouver, about 12 minutes from the lake. During my last years at Willamette SC, I had to add about 10 minutes more to the trip, on average, from year to year. The trip truly sucked at the end, and was very unpredictable. That said, the Daysailer fleet at WSC were the greatest folks to hang out with. But sailings conditions on the Willamette are awful compared to Vancouver Lake - shifty winds, loads of traffic, noise and constrained space. The drawbacks to Vancouver Lake are shallow depth and stagnating water, with attendant algae blooms. The milfoil is a new problem, but the first treatment to knock it back is already approved, paid for and scheduled for October when water conditions permit. There are a couple of Daysailers on Vancouver Lake that get out occasionally, a number of Lido's that rarely do, and of course, the Lightnings. You get an active racing fleet, tons of available advice and expertise, and one of the most beautiful dinghies on the water. However, I'd also consider picking up something extra that the girls can blast around in on their own and that you can singlehand when getting a Lightning out isn't convenient or crew isn't available. RS Fevas and Teras are made for teenagers, indestructible and are great to singlehand. But a Laser or anything you can toss in the water quickly would do the trick.
Go for time on the water, and try to reduce any factors that might get in the way. BTW, I'm not a Lightning owner or a racer - I have an Aero and a Weta at Vancouver Lake and get out about as much as anyone. But if I raced, I'd have a Laser and a Lightning.