vlans - are they worth it (opinion thread)

Hi all,

I have a home network (cca 20 devices at full load). Basic topology:

                                                            VOIP gateway (2x)
                                                               |
WAN -- Router -- switch1 (apartment 1 ) - switch2 ( building hub )- apartment 2
               |                     |
              devices           apartment 3

Router is a Gentoo box.
Apartments 2 and 3 are completely out of my control.
I'm thinking about replacing switches 1 and 2 with managed switches, to create vlans in order to logically separate apartments.
Being a complete newbie to VLANs et al, I borrowed a managed switch, played with it a bit already, and am left wondering whether it is worth the setup complexity.
The main reason I'm considering this is L3 separation of networks (mainly for VOIP gateways)

The other main advantage I see is that I could put the WAN access on the main switch, with the router anywhere else on the network :

                            WAN                     VOIP gateway (2x)
                                \vlan1                /
Router -- switch (apartment 1 ) -- switch ( building hub ) -- apartment 2
                     |                              |
                  devices                   apartment 3

Any input would be welcome, me not being a network guru, I'm wondering if I'm overthinking/overcomplicating this...

Thanks,

PS : I hope the ascii art looks as it should, I haven't found how to make use of <pre/>
PPS: Not 100% sure this belongs in this forum, move if appropriate.

If you have no control over what's being plugged in at the various apartments then you need to segregate traffic, either physically or with vlans.

All it takes is for a rogue DHCP server to be plugged in anywhere and you could theoretically open all DHCP guests on the network with the rogue DHCP server being able to redirect all traffic from hosts through an arbitrary default gateway.