"so ye like nice expensive cels"

Ya, I think every cel collector likes expensive 
cels. Not referring likes to buy expensive cels, 
just likes to enjoy the sight of expensive cels

"only if you own alot of kenshin cels and plan 
on selling them"

Not exactly, the value of a cel also makes an 
owner feel good about that cel along with it's 
beauty.  The prices of a cel pretty much reflect 
the current worth of that cel. Especially, when 
we are talking about cels selling by dealers like 
Animanga or Taro. I believe both the collectors 
and sellers want to see their cel prices go up 
instead of down. 

Only if you are a buyer, you want to find some 
cheap prices for high-end cels. But that rarely 
happens. On the other hand, I would be in doubt 
if someone is selling a Kenshin Opening cel for 
$100 - $200. Is the cel damaged or fake?

"wouldn't they already be worth collecting if 
you love the show, why does a higher price 
influence you to buy it more"

Like I said before, high prices usually go along 
with high-end cels. It's unavoidable if you are a 
high-end cel collector. Also, notice I mentioned 
two most common reasons for a collector to 
collect a certain series, value and your love for 
the show. These also apply to me, not only the 
value.

"also people rather the prices stay low, so they 
can buy more cels from there favorite series and 
make it easier to find better shots of there 
favorite chacaters"

Ya, I guess so in a sense, but unfortunately it 
doesn't work that way. First of all, the 
probabiliy of people having the same favorite 
anime show is statistically high. There is a 
certain pattern to all business economy. 
Basically the same would be said for cels, but it 
varies slightly. Highly demanded product will be 
pricey and get sold more, but over producing this 
product will cost over production and loose its 
value. On the other hand, collector's items, 
especially cels, are different. There are only a 
certain amount available. So, highly demanded 
cels will cost more and get sold more, and become 
rare, which becomes even more pricey. This 
phenomena applies dramatically for popular shows 
which are enjoyed by many, like Kenshin. Unless, 
the cels were rare to start with, like 
Evangelion. 

So, although buyers love to buy high-end product 
with cheap prices, and rather the prices same the 
same, unfortunately, the economy just don't work 
that way!