I'm not really an authority in this area, but I have been talking to many industry insiders during fairs we once in a while have to visit to keep in touch with the companies.
1) Will DVD writers' speed will go up some more, say 8X.
Current speed of DVD+R is 8x, will probably go to 12x this spring and will likely end at 16x, but I have no clue when this will happen.
2) Will the price go down as low as CD writers.
I think that it's likely that prices will drop even more the coming months indeed, if it'll be as low as CD recorders, I doubt a little.
3) Are they really worth it ?
It depend on what you want to do, for databackups they are of course with 4.7GB able to store a lot more data. If you are making home movies, I'd say what's still stopping you? And of course chances are that there will be more games and movies of which you would like to create a backup.
4) Are DVD medias will be cheaper ?
You can be pretty sure about this, currently there is already a lot of production of DVD recordables, but it is very likely that the production capacity in Taiwan will be rapidly expanding the coming months, resulting in much lower prices. There is not really a reason why DVD recordables are currently relatively expensive (Compared to CD-Rs)
5) If I should get one, which writer should I get, LiteOn Dual DVD writer ? I like to backup DVD movies.
I can't really advice you what DVD writer to get, but I'd still go for a dual format at the moment. It seems that a DVD+RW writer will not dissapoint you, for now and in the future, but DVD-RW is still sold a lot, and you be better safe then sorry