I think you make an interesting point.
Firstly though, be aware that engineers only really give a 'marginal' improvement on the weapons / modules you have. You're better, really, earning money to upgrade your ship through standard upgrades, in regular shipyards first. If you want to grab an extra five percent you can then go to an engineer.
At the moment you need both engineering commodities, and materials to engineer ships beyond level one. That looks likely to change, with the removal of the commodites (that's in beta right now) but you will still need the materials. Suggest checking out
http://inara.cz/galaxy-engineers will give you some clues for CURRENT blueprints but as I say, these are a little bit up in the air at the minute)
I suggest building up a stock of materials. Missions do give them so, while you're earning money for modules, see if you can pick up some random materials at the same time. The first time you visit an engineer then, you might have to take what you can get (and take what you can get is definitely the nature of missions) but you can look at specific blueprints later as it's a bit more advanced to actively work on getting a specific blueprint ready.
One way you could look at it is you're not really 'exploring' if you do go down to a surface in SRV looking for materials .. you're "looking for materials" (scavenging)? It's a bit of a different mindset is what I'm saying but if you're main focus is going to be on money you can pick up good salvage on planet. Cannisters of platinum, gold, narcotics, weapons, are smuggler's gold dust. Then if you 'happen to see a rock while looking for cannisters' .. bust it open, grab materials and carry on.
You can get materials mining too, though that takes a specialist ship loadout so it depends how much cash you have, what ship you're in etc. because mining's not great fun without collector limpets (if you like trading though, you might enjoy it, with them). I'm a miner and have materials coming out of my ears as a total byproduct.
Treat materials like that though, a byproduct, grab them if you see them, build up a stock and then you have more choices in engineering. Credits are key though. Why engineer an E grade module if you expect to work towards an A grade, when you'll lose the engineer's modifier (unless you store the module but by then really it's obsolete).