I disagree - unlike classical timepieces the expense here is what inside the watch, ie the processor etc.
Always buy the latest since that’s what lasts longer. This is especially true with a new product like the watch which is constantly being updated with tech improvements.
Don’t buy the Series 2, go with the series 3.
It is, of course, both inside and outside with the Apple Watch, which is what makes it a tricky value proposition.
My S0 aluminum is slow, but generally still gets the job done for my uses (no 3rd party apps at all). It does, however, have two noticeable screen scratches that bother me. If I were to upgrade it would be for this more than the speed at this point.
Speed vs. aesthetic durability. Take your pick or spend more money.