You worked really hard. So what?

Just because you “work hard” doesn’t mean your users find your product relevant or useful.

In other words, does "delighting” your users necessarily come mainly from "big" solutions that involve a lot of engineering resources, time and/or money?

I personally think this approach is misguided - often to the extent that it's downright wasteful (and even measurably harmful to your progress).

Concentrating only on "going big" draws the wrong conclusion that increasing effort necessarily equates to increased user satisfaction.

As you know, working harder and/or more doesn't necessarily mean better results.

Instead, my view is that the focus should instead be on producing desired outcomes for users that they find meaningful.

Note the distinction here: it's not about focusing on feature size, but instead on generating end results valued by your users - regardless of feature size. 

In the course of building your product, some of these features will certainly be "big" - but others will be low (or moderate effort) but punch well above their weight.

In other words, it's more so about features with high leverage. 

And leverage is not always necessarily tethered to the effort required to bring a feature to fruition.

Features that require relatively low or moderate effort but meaningfully impact user experience include:

• Read receipts for messaging apps
• Password visibility toggles
• Toggling between list and grid views
• Auto-fill from previous entries
• Collapsible web content sections
• Instant tooltip information upon hovering

What's more, "delight" can come from stacking multiple low-effort features, as well as combining them with high (or higher) effort features. 

In other words, "delighting" your users isn't always about the "sweat of your brow".

Instead, it's more about producing specific outcomes - independent of your effort -that meaningfully impact their professional and personal lives in ways that result in greater convenience, easier assimilation of information, better decision making or anything else that is important and relevant to them.