What's your favourite part about being a lighting enthusiast?
My favourite part is the feeling you get when you find that elusive lamp or fixture that you've spent years searching for.
My least favourite part is opening a fixture and finding it infested with insects and then having to spend 3 hours making sure you've gotten them all out.

Favourite part: Finding something new, be it an interesting lamp or fixture, for the collection or in the wild.

Least favourite part: Seeing older lights replaced or just removed. Even worse if they get replaced with generic garbage, or get hacked up.

I second that.
 

Favourite 1: Knowing each fixture has a story to tell, and knowing what that story is
Favourite 2: Seeing old, worn (sometimes beaten up) fixtures still working perfectly.

Least favourite 1: Noticing the absolute abomination retrofits people think they can get away with.
Least favourite 2: Space management, especially with large fixtures.

Our favourite part is getting that box containing a new lamp and unwrapping it carefully to gaze upon it. 

The least favourite part is looking at the dwindling bank balance... 

My favourite is finding something rare or vintage still in use in the wild. Or finding that lamp/luminaire you always wanted for your collection.

My least favourite are when rare lights get removed or hacked up, the high costs of everything (ehem SOX), and finding the room to store the bulkier stuff.

@ Sammi - Tell me about it; if you hadn't noticed, it's usually my dwindling bank balance 

@ Joseph - When I see on eBay that somebody has "upcycled" something old and rare by putting [insert expletive of choice] LED's in it 

 Favorite :  Finding an extremely rare lamp or fixture !! 

 Least favorite :  Having said lamp or fixture arrive as CONFETTI !! 

Favourite: I feel very lucky to have started my interest in the early 1990s, so I remember when the blue led was a novelty, then when the little 5mm Nichia was a revolution for cavers and hikers. I saw the evolution of led lighting and how the general public changed their use of light. I knew some rural and urban street lit by mercury or fluorescent tubes, and some incandescent lamp posts in Paris around Le Louvre.

Least favourite : I'm not a technical guy and don't feel connected with the people in forums. I'm interested in people behaviours around lighting, ambiances, or sociologic aspects, this kind of things.

FAVOURITE: As above, being old enough to have witnessed mercury, low and high pressure sodium in street lighting as newer lighting enthusiasts today sadly haven’t had that pleasure!
Having all HID lamps and gear still wildly available when I started working and able to buy it all off the shelf!, again most people will never have that option now 
Being able to see and teach myself first hand with said lighting back in the day and the army of lighting catalogues that greatly helped this too!
Having fresh technologies in LED, both SMT and filament lamps now too keep the interest in lighting going today!

LEAST FAVOURITE: Collecting so much stuff that you can’t leave anything lighting alone without constantly feeling the need to mess with it all the time! 

Favourite - Managing to acquire an example of most varieties of LPS lamps 

Least favourite - The obsession with LED's and the removal of choice in what we can buy/use 

My favorite part in being a lighting enthusiast is when I acquire working rare lamps, ballasts, and fixtures in my collection while my least favorite part of being a lighting enthusiast is when I see traditional lamps, ballasts, and fixtures getting discontinued and/or banned by governments in favor of LED. For example, the upcoming 2023 ban of linear fluorescent and CFL lighting in the European Union in less than one year from now makes me feel like I have no time to get a complete set of a category of European market fluorescent lamps.