Valve retainers are not high wear items, as long as (as Jack warned) the springs wearing against them have no sharp edges.
My preference with valve train parts is to lighten them as much as can be done for a reasonable amount of money, and then use springs of "moderate" force. This is the best strategy for enabling hydraulic valve train to rev to 7200 rpm, and for reducing valve train wear in street engines that are expected to operate many miles without maintenance. And of course stainless valves and titanium retainers are the most "cost effective" manner for reducing valve train weight.
Side note: stainless steel is not that much more durable than titanium, yet the valves are much higher wear items than the spring retainers. Stainless valves give me more concern about wear than titanium retainers.
The need for light weight valve train becomes more important as valve lift (lift rate) increases and as the engine's rev limit increases. You can substitute lighter parts with stronger springs, but only to a small degree IF the engine is equipped with hydraulic tappets because very stiff springs can lead to premature tappet collapse.
On the other hand, if the engine shall be rev-limited at 62000 rpm, or if valve lift is moderate, chromoly retainers should be fine.