I've only been selling patterns for about 2 years on other sites and here on Etsy. I agree with the others about date, rarity, style, condition, cut or uncut being the main attributes that determine a patterns cost. I Google all patterns I've never sold before to see what others are asking and getting for it.
When pricing my patterns I aim for top tier pricing, meaning when I first list I list it for the most I think it can bring in giving the previous factors. If after the first 4 months on Etsy it does not sell I then "consider" lowering the price when I renew the listing. Sometimes I will then sometimes I won't depending on how many hearts it has. However hearts are not a sure indicator as to if the pattern is overpriced. Only you know how much you have invested in the pattern and how much you are willing to accept as a return on that investment.
My patterns are purely an investment, and my pattern business is a business. Sometimes I lower prices to move products so my stock won't appear so stale to returning customers; and on the more desirable or rare patterns I hold my ground and don't sell out so fast just to move it. If your store is new, it takes time to be known and for people to find you. You must be patient, price fairly and promote your store.
I often see others selling the same patterns I have within Etsy. If their price is significantly lower I either buy it (if I think I can flip it for a profit) or don't worry about it. Maybe some people won't admit to buying patterns others are selling so low but again, I'm only doing this to make money. I seen sellers selling patterns on Etsy for $2.00 and I wonder what in the world are they doing this for...I stay up at night till 4 or 5 am checking pieces, taking photos and editing, typing listings there is no way i will sell for a mere $2.00 each!
Sellers should not make Etsy a garage sale pattern outlet because we take considerably more care with our vintage items. Price your patterns accordingly for the amount of work you put in and the value of the pattern.