OP, as someone who rode the Microsoft gravy train for years, I know how hard it is to let go of that golden goose and settle for a measly market-matching index fund. It took me several years to completely switch over -- but I have never regretted it. I sleep better at night, regardless of how well Microsoft is doing now, because at a certain point, you've won the game.
Make no mistake: by having 95% of your investments in one stock, you are taking a huge risk, much bigger than buying a $1.5-million house. I agree with those who say your first priority should be finding tax-smart ways to start moving from Apple to a total stock market fund.
You say you don't feel rich. It sounds like what you don't feel is financially secure, which isn't the same thing. I recommend laying everything out in a spreadsheet or other financial tool, running some long-term projections, etc. Maybe read J.L. Collins's Stock Series website for some perspective.
I know I felt much more financially secure when I figured out my best asset allocation, moved from individual stocks to broad-market stock & bond index funds, and had some solid financial projections for the next several decades. Knowledge is power. You can't really project how Apple will do over the next 50 years, but you can make a reasonable guess about the entire stock market.
About the house itself -- I don't think it matters what you spend, as long as you can afford it without jeopardizing your family's financial future, and with the numbers you're talking about, you likely can. Don't worry about whether the Seattle RE market dips or rises, or the stock market either. If you're not selling, the prices don't matter.
Look, there are no guarantees. But there are probabilities. Microsoft used to be the killer stock. Now Apple is, and Microsoft isn't. I strongly suggest getting out of the high-risk/high-return scenario -- over a few years if that's more comfortable for you -- and into a more diversified, less risky portfolio. You've already won. Now take your winnings before you lose them.
That's what I'd do, anyway.