My husband asked a similar question of one of his older friends (father to two): "What was it like to go from one kid to two?" His friend thought for a moment, and then said, "You know, I really don't remember." I think I'd have to say the same for us when we went from 2 to 3. A couple of mothers I know have said they didn't really start to learn how to be patient until they had their fifth child. Since the shorter-term misery is likely to be forgotten in a haze of sleep deprivation, we are building our family up for the long term.
ROFL! I'm a dad to 5 (soon to be 6), and this comment really hit home. I don't remember the transition from 1 to 2, or from 2 to 3 (and so on). Here's my advice:
--going from 2 to 3 kids shouldn't push you into a larger house unless you're living in a 2-bedroom place. We're in a 4-bedroom house, and all four of our boys (ages 9 down to 1) share a bedroom. AND now that the 1-year-old has moved into the toddler bed, the crib is available in case #6 turns out to be a boy! :D
--going from 2 to 3 kids shouldn't push you into a larger car. Well, it *might* if you have a very small sedan and the car seats and boosters don't fit 3-across. But the oldest will be out of even a booster soon, so you'll be fine
--you didn't mention whether your kids are sons or daughters or one of each. If your third is the same as one of the older ones, you'll save a ton on clothes.
All that being said, finances should NOT be a major consideration in your choice to have kids (within reason). If you feel like your family is not complete with two kids, then by all means go ahead.
As for whether you can provide enough love or attention to more kids, I say "hogwash." It's true that with more kids, you'll have a harder time spending one-on-one time. That doesn't mean you love them any less, nor does it mean that they will *feel* loved any less. Heck, I'm the youngest of 9, and I don't feel unloved. Of course, I *was* the baby of the family... maybe Weedy Acres can provide some perspective on being further up the food chain in a large family :) Being a kid in a large family also encourages kids to develop independence and leadership skills--it's particularly gratifying to watch our kids make themselves breakfast on Saturday mornings when DW and I want a few minutes more sleep.
As for the other concerns:
--shuttling them to various activities: my wife managed to schedule all their swim lessons in the same time slot this summer. We generally limit them to one or two extracurriculars at a time.
--homework: I agree homework in elementary school is ridiculous. That's one of the benefits of homeschooling :)
--harder pregnancy: Yes, each pregnancy has been progressively less pleasant for my wife.
I'm totally biased on this--my wife came from a family of 6 kids, I'm from a family of 9 kids, and we're expecting our 6th, so a third kid doesn't seem like a big deal for me. That being said, having more kids *can* be stressful at times, especially when they're young and/or mischievous. But those stressful times are overwhelmingly outnumbered by the joyful times, when we play games as a family, or when the kids all collaborate on an elaborate blanket fort in the family room, or when our then-4-year-old son took it upon himself to teach his 3-year-old sister to read(!).