Shock spikes is a great solo tool. Also useful in a party if you dont have a CON, as you can still aoe it. Same for Stoneskin, on both points.
Basically, if you know you are going to have a CON with you, its not neccessary. However, there is also the matter of shield skill. It helps to keep your shield skill up if you have more than one class using one.
And as far as shock spikes as a cross-class skill: it still procs stun pretty often, and if you put points into Lightning Attribute, you can further boost the damage.
FFXI - Endyne(Asura) RDM 78, NIN 85
FFXIV - Endyne Asuran (Mysidia)
THM 18 // GLD 20 // CON 13 // BSM 17 // GSM 13
LWR 9 // WVR 13 // MNR 15 // LNC 21