Have you looked into www.portcompass.com??
They offer great excursions plus transport to Valpariso. We are using them for a Princess cruise that leaves Feb. 24th. I have emailed them with questions regarding several tours and they are very responsive and very accomidating. I got the referral from several other reviews I read. We are also doing a one day extension with them in Buenos Aries to visit the Iguasu Falls region.