It's a good idea to come up with teaser trailer shorts, just a little market enquiry and must have been fun to do for the creators. Dismissable except the 2nd (Champlooesque alternate) and 8th (Macross&Eva crossover with quality animation) ones. Still there is no harm watching it if you liked the series. There are almost no spoilers since these are imaginary what if? trailers, you can barge in whatever point you are on the series.