Kick serves are nice, but I don't think you absolutely need one. A topspin slice serve is still a very effective 2nd serve, even if it doesn't result in a funky jump that messes up opponents.
Usually, kick serves are pretty easy to read which gives your opponent the green light to step in and take your kick serve on the rise. If you can disguise it, then you have one BA serve.
As long as you can mix your serves up, whatever spins you have are fine as long as they are consistent.
I always get annoyed that there aren't consistent definitions, because issues like this arise.
What are the definitions for: (My opinions in parenthesis)
Topspin: (The topspin component of a serve. Theoretically a serve with only topspin, no side rotation.)
Slice: (The rotation of the ball causing it to bend left (for a righty) or right (for a lefty)
Kick: (Used to describe a serve that 'kicks', typically with both topspin and slice, but with an emphasis on topspin)
Twist: (See: Slice)
American Twist: (Not so clear on this one. I was always taught that this is the ********, arm injuring serve where you twist it the opposite way for someone with your arm preference. For example, a righty would use this and his serve would curve to the right like a left serve. I've also heard 'Reverse Twist', but I believe this is the same thing. Why else would they differentiate 'american twist' with 'twist').
If you have the same notions of these words as I do, your post is incorrect. A big kicker is an absolutely *essential* tool of an accomplished player, regardless of whether they use it all the time. Flat is for first serves, not consistent enough for second serves *at the high level* (where flat serves need to be very, very fast, or very, very, well placed, or a high combination of both). Slice is useful occasionally to mix things up, but typically results in less margin for error (not only do you introduce the risks associated with fast racquet head speed - shanks, you don't get the benefit of topspin dropping your ball in for hard serves!), weaker serves at a required consistency, and is far less effective in confusing an opponent than a combination of topspin and slice (a kicker).
Again, this is all assuming you play, or aspire to play at a high level. If you want to joke around and just have fun with what you have, not improving at all, then by all means, ignore the kicker. Although, to be honest, one of the most entertaining moments in tennis is when you hit a big kicker right to your opponent, and they completely whiff, get hit, or catch the ball.