Flughaven, this really needs some sort of cost/benefit analysis. In all of Europe in a year, I wonder how many aeroplanes had a serious failure after take-off with associated Communications failure with bad weather at Departure point with the need to divert to a Departure alternate? I would hazard a very wild guess at 1/10 of an aeroplane per annum (ie one aeroplane fulfilling that scenario every 10 years). So to counter that threat, every IFR flight departing a limits Departure point cluttering up the airwaves with virtually un-needed Departure Alternate information (after all in the event of an emergency and loss of contact, many eyes will be watching you on radar) that will be passing this information on air may block someone else's clearance information communication and prevent some vital piece of information getting through! So by you passing what many may feel is irrelevant safety information may cause a greater hazard to someone else that would not have otherwise occured if you had not been so conscientious. I can think of 2 accidents that have happened because of communications mixups, and I know there have been very many more- Tenerife 747s and Milan MD9.
I would say it is not at all needed. If you have to pass that information, put it on your IFR Flight Plan, but don't waste radio time on it. It will be obvious to your contollers that the weather is bad and you can't come back.