For myself, I try to give each house a sense of 'advantage' of one form or another and of varying degrees of magnitude. It's what makes belonging to a house feel like it means something. Tremere are the ones that get the most out of house support, but it shouldn't come at a 'cost' to the player outside of that generated by stories.
For my sagas, foci are common. Not ubiquitous, but common. One in three magi has a focus of some sort. Thus, if all the player magi have foci, that's hardly an issue.
For focus-less magi, gaining a focus can often be the result of a positive twilight experience.
From an entirely running-a-game perspective, foci give players a direction for specialisation. Specialisation is a good thing - it encourages diversity and gives each person an area they can shine in. It gives a sense of direction and narrows the scope of choices. Likewise, specialisations for NPCs give a nice bullet-point that summarises them - which can in turn factor into OoH lore rolls and the like. This makes them easier to challenge to certamen or wizard's war, or as allies or mercenaries to a player group. This - again - is good. It means the tribunal becomes more interactive, and thus makes it feel more alive.