IO540,
Whatever the forecast, there is still nothing wrong with looking for yourself.
It's a thinking game and when ice is thrown into the equation your actions must have a good out or plan B (and C if you like).
What a plonker I'd have been to have sat at 4,000' with tops at 6 or 8 or 9 for that matter.
I may even also have got to 10,000 still IMC WITHOUT getting any ice. You just don't know.
The aircraft I was flying can get to that altitude in less than 5 minutes which doesn't represent a high risk for climbing to have a look, especially with the high 0c level.
As it was, the conditions at 10,000 were difused tops, no horizon, just a pale shade of white and there was no further ice accretion.
I have mentioned convective cloud in an earlier post and the ice exposure was very brief. These clouds often have limited lateral extent. In freezing rain or drizzle, which you can get in positive temperatures, where you are flying along quite happily below a warm front.
There was nothing wrong with that decision.