When you buy a pass, seat reservations are not included. This also applies to Germany.

Reservation on X2000 Service  Denmark/Sweden were slightly more expensive in 1st class as in 2nd class (on morning depatures was a small breakfast included before Covid) 

In my experience you didnt get much for 1st class in these countries except maybe the entry on  SJ (Swedish) and DSB (Danish) rail lounges at major stations :) 

In most cases there is a flat price for whatever type of just-REServation, be it 1st or 2nd. and it will NOT be free. 1st is generally only available on the major IC/long-dist trains and NOT on nite-trains (as seat).

In DK there is/was also free cf/T/OJ in DSB-IC trains, only in 1st.

Note : für die DE-Sparfuchse: with a 1st pass NO access to DB-lounges!

correct no lounge acces in Germany wih a 1st class pass :/ 

but there are other countries like Austria,Hungary,Sweden,Denmark,Netherlands that offer nice lounges ;) 
Ceske Drahy (Czech Rail) too and here you can get in even with a 2nd class pass you just need a reservation for a fast train (these can be bought from just 1€) 

In my experience UK, Sweden and Budapest have one of the best lounges (the provide even some snacks ) 

same apllies for some trains in the UK as you get here in 1st class a complimentary meal and drnks ;) 

I'll have to test those then. I like the Eurostar lounge in Brussels and the one in Wien Hbf :)

Yeah Wien HBF is good just was there this morning (to catch a free breakfast )  currently in the CD Lounge in Prague waiting for the Eurocity back home :D 

Here the offer of the MAV Lounge in Budapest (you can even pay to get access for max. 4hrs ) https://www.mavcsoport.hu/sites/default/files/upload/travel-offer/document/public/a5_keleti_bl_05-01_22.02.pdf