SRX210 has st0.0 configured with 10.1.124.251 address. I dont this it is needed, can you remove it? Note that you need to leave the "family inet" configured on that interface.
So far I have checked the following.
+Topology:
st0.0 st0.0
(10.0.0.0/8)------SRX210-(ge-0/0/0:24.106.47.110)------Internet----(fe-0/0/0)-SRX100-------(10.1.124.0/24)
static dhcp
Brookfield Greendale
+Junos
RootsBrookfieldWI-SRX210he: 12.1X46-D45.4;
RootsGreendaleWI-SRX100h: version 10.4R4.5;
+IKE configured as host-inbound-traffic on the untrust zones.
+IKE-IDs configured properly for phase 1.
+Proxy-IDs: any,any,any due to route-based VPN, so they match.
+VPN configuration match correctly (cant tell about configured pre-shared-keys because they are encrypted in the config)
+Static routes configured and pointing to correct st0.0 interfaces.
+st0.0 interfaces are configured with family inet.
Try configuring again the preshared-keys to a common value:
SRX100:
#set security ike policy IKE-POL-GREENDALE-ATT pre-shared-key ascii-text junos
SRX210:
#set security ike policy ike-policy-GD pre-shared-key ascii-text junos
After those two changes, please collect again:
> show security flow session protocol udp destination-port 500> show security ike security-associations> show security ipsec security-associations> show security ipsec inactive-tunnels