There is more of a difference between the SP and LS than just the fact that one has a phono and the other not.
A good reference site is the ARC database site for looking at the history of their products. This site has a strange address and reads "www dot arcdb dot ws"
Here you can look at a history of when products came out and at list prices.
For example, there is a LS16, LS 16MKII, SP16, SP16L. There are similar lineages for the LS17/SP17 and SP17L. In these instances the LS vs. SP differences are a quality and performance based with the LS being considered a higher level product (ie. LS16 vs. SP16L and LS17 vs. SP17L).
Another nice aspect of this site is that you can get true list prices for the components as such prices are often misquoted in ads on Audiogon (obviously to the high side).
For example, the SP16L (without the phono board) had a list price of $1,995 from 2001 through 2006 and a price increase for its last year of production to $2,495 for 2007 year only.
The LS16 had a list price of $2995 when it came out in 1999 and never had a price change. The LS16 MKII was priced at $3,495 and ran from 2001 to 2006 (I believe) and never changed its list price.