Short answer: they can be, but they're a volatile, illiquid alternative asset — not a savings account. Here's the honest breakdown.
What has actually held value
Sealed special sets (short print windows + theme demand), blue-chip nostalgia sealed like 151, and graded 10s of marquee chase cards. These are the most consistent performers — see best cards to invest in.
The risks nobody mentions
Reprints can crater a card overnight. Sealed can sit illiquid if a set falls out of favor. Grading is a gamble plus a fee. And the resale premium you pay on day one is pure downside — buy a hyped box at 2× retail and it has to nearly double just to break even.
How to lower your downside
Buy at retail, not resale — that's the single biggest edge. Run listings through the resale calculator, and catch sealed at MSRP with QuickCatch so you're not underwater on day one.