Normal beehive and normal stove works fine. Is there an upside to building the improved variants? There is no info on this ingame or in the wiki…
I believe improved beehives have more space in them to gather more honey, as most improved stuff do.
Nothing really. 500 honeybis morenthan younwill ever need tbh. Both are cosemtic mainly.
Improved Beehives have insane amounts of HP for what they are, so they’re harder to break than regular ones too.
There is, but sometimes it is hard to spread the small details everywhere someone might look for them because there are so many pages. See this page to get what you are looking for.
To answer your specific questions, Improved Stove gets an additional 25 inventory slots and Improved Beehive has double inventory and double production speed.
Thanks for the link, I was unaware that stoves and even fireplaces gave decay reduction. Good to know. 
People use to have the improve beehive as a blockcade due to high hp n low cost
And this is the issue with placeables because there isn’t a formula to them. The HP is ridiculous for a beehive. We all know it it is. So how did it get there? It’s a 20 fold increase of HP from the standard to the improved. the improved stove goes up 6 fold. This tells me that HP is designated in a bubble without any consideration of what similar objects are like. A think a 5 fold increase from the standard to the improved isn’t that problematic and remains consistent. You only need to determine the base HP and the formula would do the rest. T1 craft tables to T2 improved craft tables to T3 monsterous craft tables transitions would all be formulaic and therefore only the T1 needs to be considered in designing the numbers. Its a win win win but lots of legwork in the beginning.