I have tested 60 FPS Vs 30 FPS using 2 similar joovuu X cameras, and to be honest i dident fine much in favor of one over the other, using plate capture as a reference under different conditions i found that if one caught a plate the other would also do the same.
Normally cameras drop down to a 1:30 second exposure, the longest you can have for 30 FPS footage, and so footage are brighter, but with movement ( which dashcams are pretty much all about ) you then see motion blur at so long exposure times.
Using a 1:60 second exposure timing in spite of a better sensor and only half the time for the sensor to collect light, in low light its still way too fast for capture of small details, and in daylight it do not really matter unless its in that tiny time frame of day where day transition to night.
Its sort of the same predicament you get comparing a dashcam with the latest and best low light sensors Vs a camera with last seasons good low light performer sensor.
The new sensor will make you see more in the video, but if you hit pause and forward thru the footage frame by frame you will also see that all the extra you can see in the footage are not really something you can use for anything.
So while i do recommend to go for the latest sensor cameras, it is just due to they are more easy on the eye watching low light footage, there might be a little gap in the transition time from daylight into evening where a camera with a new sensor will be better than a camera with last years sensors, but its my firm belief that this time frame are short and marginal.
This time of the year here in Denmark and with cloudy days like we have most of the time, well i cant capture a plate unless we talk slow moving traffic, but on my reference highway speeds of 80 km/h for me and oncoming car its a big old no go.
ATM sun rise at 8 in the morning and set a little after 4 in the afternoon.
But while cloudy are not a problem in the summer time, then the sun are just too far away this time of the year for it to work on a cloudy day now.
So i stick with 30 FPS all year all day.
Other swear to 60 FPS, but personally i dont feel the need for using that.