I'm someone who maximizes point with airlines, hotels, and even parking so here's my advice and experiences. The last three trips to Europe have been mostly in United Business class using miles, several nights of free hotels , and free parking during the last two trips.
You are in California, so depending on whether you fly out of SFO or LAX, which airline has the most flights to where you normally travel to? I travel a fair amount on business, mostly to from Chicago, so fly either United or American. I try to avoid other airlines as to focus earning miles on either of those two airlines.
I originally obtained a Capital One card since there were no international transaction fees. On Capital One, I believe I earned about 1.25 points for every dollar spent. So if you charge $25,000, you earn 31,000 points. That equates to a $325 plane ticket (domestic). So figure a trip to Europe at $1500 RT per ticket, that would take 150,000 points for that ticket (over $100,00 in spending). Not a great deal. And you can't partially pay for a ticket with points vs. money.
Since we travel mostly on United domestically, for either work or pleasure, we signed up for a United Explorer card. The explorer card has zero intl transaction fees, acts as primary insurance for car rentals, and gives you priority boarding and free checked bag. For every $$ spent you receive one mile. And yes a lot of miles for signing up (30K -50K). So if you charge everything on your card (insurance, cable, cellphones, groceries, travel, etc) and spend over $25,000 in a year, you receive 10,000 bonus miles. So in year one you could be looking at 85,000 miles without getting on a plane. Throw a couple domestic trips in there and you are close to 100,000 points. A round trip to Europe in economy saver is 60,000 miles. So what if there are two of you? Have the second person sign up for his/her own card (wait for the 50K signing bonus).
If you need to top off miles to get the saver award, buying miles is an option. Here's an example. You are short 20,000 miles for 2 saver tickets (120,000 miles). You can buy 20,000 miles for $700 at full price. So with miles earned and purchased, you end up with two RT economy tickets for $700. Not a bad deal. United runs specials on miles purchases on occasion.
We like to use miles for business class if possible. So in December, I'd already used my miles balance for my return trip from Paris. So when I found a business seat for 57,500 points to Paris I jumped on it. United had a special on miles, so for $950, I purchased 52,000 points and a seat in business. Total airfare- $950 and 30,000 miles for 1 one way in business and return flight in economy. Well worth the miles purchase.
Again, since I travel for my job, I earn points at the parking lot near SFO. So on our 16 day trip to Europe in May, parking is free.
As far as hotel point/credit cards, I find that the airline cards are a better deal, and just accumulate points for actual stays at Hilton or Marriotts. In May, we have 2 nights booked at a Hilton for free. Last month we stayed at a Marriott for free in SF.