Improving RLH by itself isn't good enough. If you really want to know whether to include an interaction I suggest you use the Model Explorer. This is free software you can download here: http://www.sawtoothsoftware.com/support/downloads/tools-scripts
For estimating WTP in the presence of interactions, I recommend using the share equalization approach. Run a simulation with two concepts. Have these be identical except as described below and have them be realistic concepts that might contain your attribute and level of interest. Have one of the two (otherwise identical) concepts NOT contain the attribute level you want to value and have the concept appear at some price X. Have the other concept contain the level you are trying to value and keep increasing the price (X) until the two concepts have equal shares. This is the share-equalizing price estimate of WTP.
You can do this in more involved ways if you like (e.g. put these two concepts in a full competitive set of concepts to capture the effects of competition) but the logic is the same - concept A without level of interest and at a lower price versus concept B that HAS the level of interest but at a higher price. The difference in price between the higher price with the level of interest and the lower price without it is an estimate of WTP.