Mark, most of us would not drive in the rain locally, but sometimes on long road trips you just can't avoid it. I use my Intermeccanica for pleasure traveling and have driven in heavy rain while the interior stayed bone dry. Not just a short drive... but in heavy showers and storms from AZ through NM, TX, and OK. I have also driven it in the snow in Canada and Kings NP and stayed dry and warm. Locally we have been caught in rainshowers on day trips and then at Knotts 05 my Speedster sat out overnight with the top up in heavy rain without a drop getting inside, including the door sills and the areas behind the door windows.
Again, I don't plan on driving in the rain... but my Intermeccanica Speedster is definitely able to travel dry inside... the two speed wipers work very good for a Speedster and using IMs exhaust and heater boxes witha two speed booster fan unit (*under dash with defrost)with electric two stage seat heaters I can travel in sub 32F temps and stay toasty.
The IM Roaster seals even better, but my experience has been positive with the IM Speedster. NO sales pitch... just sharing my experience. Many owners seldom drive in the rain or they live in So Cal where the weather is more favorable and so top sealing isn't an issue for them. 99% of the time it isn't for me either. I just wanted a car that had the weather capabilities because of the distances I drive on some trips. IM meets that requirement for me.
I'm sure the SAW Cabrio owners can share with you their experience. "Hoss" has traveled cross-country USA east/west and north/south and so it probably seals up pretty good too. I second Lane's suggsetion that you go to the east show and check out the cars and meet some owners. All of the cars are fun and there's very few other custom car or bike markets that can match 356 replicas for the bang/buck ratio. As far as weather sealing... there are owners that have never had the top up on their cars, and they drive them as much as anyone else... so it just comes down to driving habits/planned use.