As you know you can guest whoever you like into the lounge as long as they’re on a OW flight at Heathrow - entirely your prerogative. However this situation really does come across as a bit odd; you probably didn’t mean it but language like ‘don’t have the means’ is quite patronising, and if someone came up to me and made me feel like ‘the poor person in economy’ I wouldn’t be overly impressed.

Why not just enjoy your trip to the lounge with the wife before your flight? Have a great time in Germany, fantastic place to spend new year!