3D Design is not as hard as you might think. Modern tools are intuative and pretty full of features. The hobbyist can design some pretty useful stuff that can be tested, made and used with confidence. It just needs a lillte bit of thought to get your head round the way it all works.
Making your own PCB's doesn't mean you need to suffer with wierd toner transfer techniques, nasty chemicals and a hit and hope metjod. Design tools can help you make a professional looking PCB straightforward. Just like mechanical design. Its all about the software.
Hasn't everyone got a 3D printer now? Mine is very basic and yet it is still very capable. You don't need to break the bank to get one that gives you good parts. If you don't fancy buying one then there are services that will take your designs and turn them into parts.
To get started, I recommend Onshape as a piece of software. Well its not even software really as its a browser based design tool. Nothing to download and no updates required. Its also FREE! I've even desined something on my really crappy android tablet.
Getting your head round solids modelling is not as hard as you might think. It all starts with a 2D sketch and adding or subtracting material to form a part or make a hole. Save yourselve the hassle and avoid surface modelling. Here is a bit more detail.
I'm a big fan of Open Source and use it where I can. I tried and tried to get my head round KiCAD but it just didn't click with me, so I reverted back to the software I started on, Eagle. Just like mechanical design it has its own way of working. Schematics and PCB's are the two main elements of the software but be aware the hobby user, like me is not the main target for this software ad the features might be a bit overkill. Have a look at the extra stuff here.
Ok, so I bought a printer. I can print soem pretty simple stuff and my da Vinci mini w is probably laughed at nowadays. To be honest I'm not fussed, it knocks out useful stuff. If fixed my shower, made antenna adapters for paint poles and printed a telescope. I'm pretty sure that makes it useful. One of the biggest collections of stuff that is useful is Thingiverse. The best bit is that you barely need to design anything :-)