TL;DR version: Worth every penny. Stop reading and book it.
As Texans with only passable Spanish and zero Portuguese, we decided that the private tour was the way to go for us as a combined tour would also need to include these languages for the Brazilian tourists who flock to Chile. That said, after spending the day with him I have zero doubt that Mauricio would keep English-speakers in a mixed group informed equally well. His language skills are quite impressive.
Our private tour started with an early morning stop at the Emiliana Vineyards in Casablanca. It was a timely stop as it's about halfway between Santiago and Valparaiso/Vina so we were able to get out and stretch our legs. We visited the pristine grounds, my girl and I shared a glass of 9AM wine (Hey! It's vacation!), and soaked in the view. As we were traveling internationally with only carry-on luggage, we were unable to leave with any bottles. Very sad.
Anyway, we jumped back in the (very nice) van to continue our trip and arrived in Vina del Mar about 30 mins later. Both cities are on the water, but the views in Vina are spectacular and Mauricio made very sure we didn't miss any of them. His knowledge of the area ensured that we saw as much as possible in the time allotted without feeling rushed (at all). TIP: Ask Mauricio to eat lunch in Vina...I've included pix of the lunches girlfriend and I had...both were "amazeballs" as the kids would say. I don't remember the name of the joint, but point Mauricio to the pix or this review and he will know.
After lunch in Vina, we jetted over to Valparaiso to check out the famous graffiti and the city center. Once again, Mauricio knew exactly where to take us for the best photo opportunities and historical tidbits. He also took us to visit the home of the Nobel prize-winning poet, Pablo Neruda, the view from which makes it clear how he could be inspired to write his beautiful and seminal "Twenty Love Poems and a Song of Despair".
In closing, I cannot recommend this tour highly enough. Mauricio is as gracious as he is knowledgeable and his only care is the comfort and enjoyment of his clients.